Fix fftw /bigobj warnings

Author: timothyschoen

Libraries/fftw3/CMakeLists.txt

@@ -313,7 +313,7 @@ set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
 add_library (${fftw3_lib} ${SOURCEFILES})
 target_include_directories (${fftw3_lib} INTERFACE $<INSTALL_INTERFACE:include>)
 if (MSVC AND NOT (CMAKE_C_COMPILER_ID STREQUAL "Intel"))
-  target_compile_definitions (${fftw3_lib} PRIVATE /bigobj HAVE_UINTPTR_T=1)
+  target_compile_definitions (${fftw3_lib} PRIVATE $<$<COMPILE_LANGUAGE:CXX>:/bigobj> HAVE_UINTPTR_T=1)
 endif ()
 if (HAVE_SSE)
   target_compile_options (${fftw3_lib} PRIVATE ${SSE_FLAG})