Fix up FC_LIKELY macros

__builtin_expect returns the same type as the expression,
so enforce that we pass in a boolean expression.

Pointed out by Emmanuele Bassi.
10 jobs for speed-up-family-matching in 6 minutes and 41 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #4266205
gst-macos-10.15
meson macos

00:00:49

passed #4266202
meson-mingw-w64-build

00:04:22

manual #4266206
docker windows 1809 allowed to fail manual
meson msys2
passed #4266200
meson-shared-build

00:04:35

passed #4266201
meson-static-build

00:03:32

passed #4266203
docker windows 1809
meson vs2017 amd64

00:01:11

passed #4266204
docker windows 1809
meson vs2017 x86

00:01:07

passed #4266199
mingw-build

00:05:35

passed #4266197
shared-build

00:06:41

passed #4266198
static-build

00:04:42