FFmpeg: pass minimum deployment target as extra compiler flags

When building on iOS, the minimum deployment target was only declared as
linker flags for the libary. However the flags can affect the run-time
features by potentially enabling APIs or affecting codegen if the
compiler can assume that certain CPU features are present.
We should therefore pass the minimum deployment target as compiler flags
as well as linker flag.

Pick-to: 6.10 6.8 6.5
Change-Id: If9b96fb31bf4173da2e4c574c1c080be075851b8
Reviewed-by: Nils Petter Skålerud <nils.petter.skalerud@qt.io>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit 1a9daf1574)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

coin/provisioning/common/unix/install-ffmpeg-ios.sh

@@ -53,6 +53,9 @@ build_ffmpeg_ios() {
     --cc="xcrun --sdk ${target_sdk} clang -arch $target_cpu_arch" \
     --cxx="xcrun --sdk ${target_sdk} clang++ -arch $target_cpu_arch" \
     --target-os=darwin \
+    --extra-cflags="$minos" \
+    --extra-cxxflags="$minos" \
+    --extra-objcflags="$minos" \
     --extra-ldflags="$minos" \
     --enable-shared \
     --disable-static \