I applied the head

   commit ce249d880969111384d17f744687e427c843f1d4
   Merge: 8a6b7a4 0e517e4
   Author: Eugene Wissner <belka@caraus.de>
   Date:   Tue Apr 10 15:37:32 2018 +0200

       Merge pull request #647 from belka-ew/gdc-49up

       Merge branch gdc-5 into gdc-4.9

of branch gdc-4.9 on top of gcc-4.9.4 and got this error:

/bin/sh ../libtool --tag=D   --mode=compile /scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/gdc -B/scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/bin/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/lib/ -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/include -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/sys-include     -O2 -g  -nostdinc -pipe -Wno-deprecated -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/libdruntime -I ../libdruntime -I . -c -o std/net/curl.lo /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/net/curl.d
libtool: compile:  /scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/gdc -B/scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/bin/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/lib/ -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/include -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/sys-include -O2 -g -nostdinc -pipe -Wno-deprecated -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/libdruntime -I ../libdruntime -I . -c /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/net/curl.d  -fPIC -fversion=Shared -o std/net/.libs/curl.o
/scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/math.d:8040:47: internal compiler error: Speicherzugriffsfehler
             return cast(Unqual!T) (T(1) << bsr(val) + type);
                                               ^
0x9e3b0f crash_signal
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/toplev.c:337
0xeb7af0 htab_hash_string
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libiberty/hashtab.c:839
0x7bc0f7 external_ref_hasher::hash(external_ref const*)
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7510
0x7bc0f7 hash_table<external_ref_hasher, xcallocator>::find_slot(external_ref const*, insert_option)
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/hash-table.h:505
0x7bc0f7 lookup_external_ref
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7538
0x7bc19d optimize_external_refs_1
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7576
0x7bc1c8 optimize_external_refs_1
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7580
0x7bc5ed optimize_external_refs
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7630
0x7bc9a5 output_comp_unit
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:8816
0x7d7319 dwarf2out_finish
   /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:24301
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.

Is GCC 4.9 still maintained?

On Saturday, 5 January 2019 at 22:27:49 UTC, kdevel wrote:
> I applied the head
>
>    commit ce249d880969111384d17f744687e427c843f1d4
>    Merge: 8a6b7a4 0e517e4
>    Author: Eugene Wissner <belka@caraus.de>
>    Date:   Tue Apr 10 15:37:32 2018 +0200
>
>        Merge pull request #647 from belka-ew/gdc-49up
>
>        Merge branch gdc-5 into gdc-4.9
>
> of branch gdc-4.9 on top of gcc-4.9.4 and got this error:
>
> /bin/sh ../libtool --tag=D   --mode=compile /scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/gdc -B/scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/bin/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/lib/ -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/include -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/sys-include     -O2 -g  -nostdinc -pipe -Wno-deprecated -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/libdruntime -I ../libdruntime -I . -c -o std/net/curl.lo /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/net/curl.d
> libtool: compile:  /scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/gdc -B/scratch/mockbuild1/bld-4.9.4/gcc-objdir/./gcc/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/bin/ -B/scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/lib/ -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/include -isystem /scratch/gcc-4.9.4/x86_64-unknown-linux-gnu/sys-include -O2 -g -nostdinc -pipe -Wno-deprecated -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src -I /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/libdruntime -I ../libdruntime -I . -c /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/net/curl.d  -fPIC -fversion=Shared -o std/net/.libs/curl.o
> /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libphobos/src/std/math.d:8040:47: internal compiler error: Speicherzugriffsfehler
>              return cast(Unqual!T) (T(1) << bsr(val) + type);
>                                                ^
> 0x9e3b0f crash_signal
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/toplev.c:337
> 0xeb7af0 htab_hash_string
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/libiberty/hashtab.c:839
> 0x7bc0f7 external_ref_hasher::hash(external_ref const*)
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7510
> 0x7bc0f7 hash_table<external_ref_hasher, xcallocator>::find_slot(external_ref const*, insert_option)
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/hash-table.h:505
> 0x7bc0f7 lookup_external_ref
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7538
> 0x7bc19d optimize_external_refs_1
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7576
> 0x7bc1c8 optimize_external_refs_1
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7580
> 0x7bc5ed optimize_external_refs
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:7630
> 0x7bc9a5 output_comp_unit
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:8816
> 0x7d7319 dwarf2out_finish
>    /scratch/mockbuild1/bld-4.9.4/gcc-4.9.4/gcc/dwarf2out.c:24301
> Please submit a full bug report,
> with preprocessed source if appropriate.
> Please include the complete backtrace with any bug report.
> See <http://gcc.gnu.org/bugs.html> for instructions.
>
> Is GCC 4.9 still maintained?


No, there is no man power nor incentive to maintain any prior versions of gcc where D is not an official frontend.

That means only gcc-9, and all future versions that will follow for will receive bug fixes for as long as they are supported in GCC's release cycle.