configure: pass the macOS toolchain flags to CCAS

Otherwise we end up with warnings like this:

> ld: warning: object file (vlc/build/modules/isa/aarch64/simd/.libs/merge.o) was built for newer 'macOS' version (15.0) than being linked (11.0)

configure.ac

@@ -276,6 +276,7 @@ int foo() { return my_array[0]; }
         CC="${CC} -isysroot ${with_macosx_sdk}"
         CXX="${CXX} -isysroot ${with_macosx_sdk}"
         OBJC="${OBJC} -isysroot ${with_macosx_sdk}"
+        CCAS="${CCAS} -isysroot ${with_macosx_sdk}"
         LD="${LD} -syslibroot ${with_macosx_sdk}"
     fi
     AC_ARG_WITH(macosx-version-min,
@@ -286,6 +287,7 @@ int foo() { return my_array[0]; }
         CC="${CC} -mmacosx-version-min=${with_macosx_version_min}"
         CXX="${CXX} -mmacosx-version-min=${with_macosx_version_min}"
         OBJC="${OBJC} -mmacosx-version-min=${with_macosx_version_min}"
+        CCAS="${CCAS} -mmacosx-version-min=${with_macosx_version_min}"
         LD="${LD} -mmacosx_version_min=${with_macosx_version_min}"
     fi
     ;;