common: autotools: define also GVC_EXPORTS

Fixes errors like this using autotools with MinGW:

C:/tools/msys64/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/10.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe: ../../lib/common/.libs/libcommon_C.a(arrows.o): in function `arrow_type_curve':
C:\Users\magja\graphviz\lib\common/arrows.c:696: undefined reference to `__imp_Bezier'

Towards https://gitlab.com/graphviz/graphviz/-/issues/2058

diff --git a/lib/common/Makefile.am b/lib/common/Makefile.am
index 7936ced56d742dccdfa182e7c1ae76d8a9da3bfc..c07b012277523cf4c303a83d4f07198b2b660109 100644 (file)
--- a/lib/common/Makefile.am
+++ b/lib/common/Makefile.am
@@ -11,7 +11,7 @@ AM_CPPFLAGS = \
        -I$(top_srcdir)/lib/cdt $(GD_INCLUDES) $(EXPAT_INCLUDES) $(Z_INCLUDES)
 
 if WITH_WIN32
-AM_CFLAGS = -D_BLD_gvc=1
+AM_CFLAGS = -D_BLD_gvc=1 -DGVC_EXPORTS
 AM_CPPFLAGS += -O0
 endif