gtest: fix poisoned exit in compile flags

visibility.h is included globally in PX4 via cmake compile flags.
It contains poisoning the exit() command which is used by gtest
to close the test application. Removing the flag for gtest compilation
fixes the compile error:
gtest.cc:4757:7: error: attempt to use poisoned "exit"

cmake/gtest/gtest.cmake

@@ -41,3 +41,9 @@ endif()
 
 # Add googletest, defines gtest and gtest_main targets
 add_subdirectory(${CMAKE_CURRENT_BINARY_DIR}/googletest-src ${CMAKE_CURRENT_BINARY_DIR}/googletest-build EXCLUDE_FROM_ALL)
+
+# Remove visibility.h from the compile flags for gtest because of poisoned exit()
+get_target_property(GTEST_COMPILE_FLAGS gtest COMPILE_OPTIONS)
+list(REMOVE_ITEM GTEST_COMPILE_FLAGS "-include")
+list(REMOVE_ITEM GTEST_COMPILE_FLAGS "visibility.h")
+set_target_properties(gtest PROPERTIES COMPILE_OPTIONS "${GTEST_COMPILE_FLAGS}")

src/include/visibility.h

@@ -86,7 +86,7 @@
 #ifdef __cplusplus
 #include <cstdlib>
 #endif
-//#pragma GCC poison exit
+#pragma GCC poison exit
 
 #include <stdlib.h>