pathplan: autotools: add define of PATHPLAN_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: .libs/cvt.o: in function `Pobsopen':
C:\Users\magja\graphviz\lib\pathplan/cvt.c:80: undefined reference to `__imp_visibility'

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

diff --git a/lib/pathplan/Makefile.am b/lib/pathplan/Makefile.am
index b2be994cbfec66c72ba2cbcf3f8cc25f9dcfb230..1f5df41c66f034179375551bcccaaaa553da9072 100644 (file)
--- a/lib/pathplan/Makefile.am
+++ b/lib/pathplan/Makefile.am
@@ -8,6 +8,7 @@ pkgconfigdir = $(libdir)/pkgconfig
 AM_CPPFLAGS = -I$(top_srcdir)/lib
 
 if WITH_WIN32
+AM_CFLAGS = -DPATHPLAN_EXPORTS
 AM_CPPFLAGS += -O0
 endif