fix(ffmpeg): only do git fetch for dependencies we're actually building

Gentoo uses the system-wide versions, so these directories are empty,
causing git to fail.

Signed-off-by: James Le Cuirot <chewi@gentoo.org>

Author: chewi

cmake/ffmpeg/_main.cmake

@@ -1,12 +1,3 @@
-# x265.pc will not be installed if their cmake cannot detect the latest tag
-# SVT-AV1 cannot determine version if the git history is not available
-foreach(repo "x265_git" "SVT-AV1")
-    execute_process(
-        COMMAND git -C "${CMAKE_CURRENT_SOURCE_DIR}/third-party/FFmpeg/${repo}" fetch --tags --depth=1
-        COMMAND_ERROR_IS_FATAL ANY
-    )
-endforeach()
-
 # the destination directory needs to be same level down as the original source directory
 file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/third-party/FFmpeg DESTINATION ${CMAKE_CURRENT_BINARY_DIR}
         PATTERN "Vulkan-Loader/tests" EXCLUDE)  # vulkan loader test files contain emojis in file names which can fail

cmake/ffmpeg/svt_av1.cmake

@@ -1,3 +1,9 @@
+# SVT-AV1 cannot determine version if the git history is not available
+execute_process(
+    COMMAND git -C "${CMAKE_CURRENT_SOURCE_DIR}/third-party/FFmpeg/SVT-AV1" fetch --tags --depth=1
+    COMMAND_ERROR_IS_FATAL ANY
+)
+
 set(SVT_AV1_GENERATED_SRC_PATH ${CMAKE_CURRENT_BINARY_DIR}/FFmpeg/SVT-AV1)
 
 if(BUILD_FFMPEG_ALL_PATCHES OR BUILD_FFMPEG_SVT_AV1_PATCHES)

cmake/ffmpeg/x265.cmake

@@ -1,3 +1,9 @@
+# x265.pc will not be installed if their cmake cannot detect the latest tag
+execute_process(
+    COMMAND git -C "${CMAKE_CURRENT_SOURCE_DIR}/third-party/FFmpeg/x265_git" fetch --tags --depth=1
+    COMMAND_ERROR_IS_FATAL ANY
+)
+
 set(X265_GENERATED_SRC_PATH ${CMAKE_CURRENT_BINARY_DIR}/FFmpeg/x265_git)
 
 file(GLOB X265_GIT_FILES ${CMAKE_CURRENT_SOURCE_DIR}/patches/FFmpeg/x265_git/*.patch)