meson: Fix build failure when compiler is not in PATH

When cross compiling gcc/clang could not exist in PATH and Meson could
be using aarch64-linux-android-clang set in a cross file for example.
10 jobs for meson-fixes in 7 minutes and 19 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #4825950
gst-macos-10.15
meson macos

00:00:48

passed #4825947
meson-mingw-w64-build

00:04:12

manual #4825951
docker windows 1809 allowed to fail manual
meson msys2
passed #4825945
meson-shared-build

00:05:15

passed #4825946
meson-static-build

00:04:24

passed #4825948
docker windows 1809
meson vs2017 amd64

00:01:07

passed #4825949
docker windows 1809
meson vs2017 x86

00:01:08

passed #4825944
mingw-build

00:05:25

passed #4825942
shared-build

00:07:19

passed #4825943
static-build

00:05:40