cmake: Specify the compiler on autotools externals

Enables CCache on externals if available.

CMakeLists.txt

@@ -605,6 +605,8 @@ if (YUZU_USE_BUNDLED_FFMPEG)
                     --disable-vdpau
                     --enable-decoder=h264
                     --enable-decoder=vp9
+                    --cc="${CMAKE_C_COMPILER}"
+                    --cxx="${CMAKE_CXX_COMPILER}"
             WORKING_DIRECTORY
                 ${FFmpeg_BUILD_DIR}
         )

externals/libusb/CMakeLists.txt

@@ -67,6 +67,8 @@ if (MINGW OR (${CMAKE_SYSTEM_NAME} MATCHES "Linux") OR APPLE)
             "${LIBUSB_MAKEFILE}"
         COMMAND
             env
+                CC="${CMAKE_C_COMPILER}"
+                CXX="${CMAKE_CXX_COMPILER}"
                 CFLAGS="${LIBUSB_CFLAGS}"
             sh "${LIBUSB_CONFIGURE}"
                 ${LIBUSB_CONFIGURE_ARGS}