Bug: https://bugs.gentoo.org/882461
Reverting commit ccf692bb38c43a38f8e9f755dd48451c6f6ad430
--- a/modules/synctex/CMakeLists.txt
+++ b/modules/synctex/CMakeLists.txt
@@ -26,6 +26,4 @@ endif()
 
 # SyncTeX uses vasprintf which is not in POSIX; thus gcc prints a warning unless
 # _GNU_SOURCE is defined. Other compilers seem to be fine.
-if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
-  target_compile_definitions(SyncTeX PRIVATE _GNU_SOURCE)
-endif()
+target_compile_definitions(SyncTeX PRIVATE _GNU_SOURCE)