Fix the process substitution doesn't work with FONTCONFIG_FILE

Don't address the real filename when a named pipe is given in FONTCONFIG_FILE.
3 jobs for pssubst in 5 minutes and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #1666990
mingw-build

00:05:16

passed #1666988
shared-build

00:04:57

passed #1666989
static-build

00:03:30