Meson: Do not wrap fccache insallation script

When passing fccache executable directly Meson does special tricks such
as modifying $PATH on Windows.

See: https://github.com/mesonbuild/meson/pull/8259

Fixes: #260
11 jobs for win-install-cache in 7 minutes and 7 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #6944514
meson android arm64 fedora

00:01:42

passed #6944512
gst-macos-10.15
meson macos

00:03:09

passed #6944509
meson-mingw-w64-build

00:04:32

manual #6944513
docker windows 1809 allowed to fail manual
meson msys2
passed #6944507
meson-shared-build

00:05:12

passed #6944508
meson-static-build

00:04:17

passed #6944510
docker windows 1809
meson vs2017 amd64

00:01:23

passed #6944511
docker windows 1809
meson vs2017 x86

00:01:22

passed #6944506
mingw-build

00:06:11

passed #6944504
shared-build

00:07:07

passed #6944505
static-build

00:06:05