Remove GC_BUILD definition from build scripts

Remove GC_BUILD definition from build scripts

* CMakeLists.txt (ADD_DEFINITIONS): Remove -D GC_BUILD (not
needed since it is defined in gc_priv.h, gc_pmark.h and
gc_cpp.cc).
* WCC_MAKEFILE (CFLAGS): Likewise.
* build/s60v3/libgc.mmp: Likewise.
* digimars.mak (DEFINES, tests/test.obj): Likewise.
* windows-untested/vc60/gc.dsp (ADD CPP): Likewise.
* windows-untested/vc60/libgc.dsp (ADD CPP): Likewise.
* windows-untested/vc60/libgcmt.dsp (ADD CPP): Likewise.
* windows-untested/vc70/gc.vcproj (PreprocessorDefinitions): Likewise.
* windows-untested/vc70/libgc.vcproj (PreprocessorDefinitions):
Likewise.
* windows-untested/vc70/libgcmt.vcproj (PreprocessorDefinitions):
Likewise.
* windows-untested/vc71/gc.vcproj (PreprocessorDefinitions): Likewise.
* windows-untested/vc71/libgc.vcproj (PreprocessorDefinitions):
Likewise.
* windows-untested/vc71/libgcmt.vcproj (PreprocessorDefinitions):
Likewise.
* extra/MacOS.c: Define GC_BUILD (before include of gc.h).
* extra/msvc_dbg.c: Likewise.
* windows-untested/vc60/gc.dsp (MESSAGE, ENDIF): Remove trailing
spaces at EOLn.
* windows-untested/vc60/libgc.dsp (MESSAGE, ENDIF): Likewise.
* windows-untested/vc60/libgcmt.dsp (MESSAGE, ENDIF): Likewise.