buildscripts: switch to clang by default
buildscripts: switch to clang by default

long overdue since gcc will get removed in NDK r18
gcc can still be enabled with the --gcc flag

mpv-android/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,mpv-android/mpv-android,jeeb/mpv-android,jeeb/mpv-android,jeeb/mpv-android,mpv-android/mpv-android,jeeb/mpv-android