CMake: only pass 'YY_NO_UNISTD_H' to Flex when unistd.h is not found

This macro tells Flex that #including unistd.h should be avoided. There is no
need for this on almost any platform except Windows, hence why `YY_NO_UNISTD_H`
is only mentioned elsewhere in the MS Build build system, not in the Autotools
build system. In the CMake build system which is meant to be used across Windows
and non-Windows platforms, we can do something more nuanced and depend on the
existence check of unistd.h itself.

diff --git a/lib/cgraph/CMakeLists.txt b/lib/cgraph/CMakeLists.txt
index 212c62f0560b3e511a56d402809376aaac03b110..83b49e3e9feb9c02530d0048667aeeaab97d1a58 100644 (file)
--- a/lib/cgraph/CMakeLists.txt
+++ b/lib/cgraph/CMakeLists.txt
@@ -2,7 +2,10 @@ BISON_TARGET(Grammar ${CMAKE_CURRENT_SOURCE_DIR}/grammar.y ${CMAKE_CURRENT_BINAR
 FLEX_TARGET(Scan ${CMAKE_CURRENT_SOURCE_DIR}/scan.l  ${CMAKE_CURRENT_BINARY_DIR}/scan.c)
 ADD_FLEX_BISON_DEPENDENCY(Scan Grammar)
 
-add_definitions(-DEXPORT_CGRAPH -DEXPORT_AGXBUF -DEXPORT_CGHDR -DYY_NO_UNISTD_H)
+add_definitions(-DEXPORT_CGRAPH -DEXPORT_AGXBUF -DEXPORT_CGHDR)
+if(NOT HAVE_UNISTD_H)
+  add_definitions(-DYY_NO_UNISTD_H)
+endif()
 
 add_library(cgraph SHARED
     # Header files