Hi,
I had the same problem regarding osx builds being broken.
The culprit is in posix.mak:

The current logic to set up SDK env var is frail and won't work for someone who has only 10.7+ SDKs. I simply had to add this: SDK=$(SDKDIR)/MacOSX10.7.sdk

but a better logic would be to test which is the latest SDK installed checking for $(SDKDIR)/MacOSX10.x.sdk, x=5..8


ifeq (OSX,$(TARGET))
    SDKDIR=/Developer/SDKs
    ifeq "$(wildcard $(SDKDIR) )" ""

SDKDIR=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs
    endif
    ## See:
http://developer.apple.com/documentation/developertools/conceptual/cross_development/Using/chapter_3_section_2.html#//apple_ref/doc/uid/20002000-1114311-BABGCAAB
    ENVP= MACOSX_DEPLOYMENT_TARGET=10.3
    #SDK=$(SDKDIR)/MacOSX10.4u.sdk #doesn't work because can't find
<stdarg.h>
    #SDK=$(SDKDIR)/MacOSX10.5.sdk
    #SDK=$(SDKDIR)/MacOSX10.6.sdk
   #    SDK:=$(if $(filter 11.%, $(OSVER)), $(SDKDIR)/MacOSX10.6.sdk,
$(SDKDIR)/MacOSX10.5.sdk)
#    SDK:=$(if $(filter 11.%, $(OSVER)), $(SDKDIR)/MacOSX10.7.sdk,
$(SDKDIR)/MacOSX10.5.sdk)

################## changed that
    SDK=$(SDKDIR)/MacOSX10.7.sdk
    TARGET_CFLAGS=-isysroot ${SDK}
    #-syslibroot is only passed to libtool, not ld.
    #if gcc sees -isysroot it should pass -syslibroot to the linker when
needed
    #LDFLAGS=-lstdc++ -isysroot ${SDK} -Wl,-syslibroot,${SDK} -framework
CoreServices
    LDFLAGS=-lstdc++ -isysroot ${SDK} -Wl -framework CoreServices
else
    LDFLAGS=-lm -lstdc++ -lpthread
endif