Fixed an incorrect check for physfs in meson.build.

This may be the cause of #5, given that it seems that physfs is what
was failing there. Will need to test this with an RC to be sure.

meson.build

@@ -78,7 +78,7 @@ if buildExec.disabled() == false
       libxml2 = cc.find_library('xml2', required: true)  # e.g., MacOSX SDK
    endif
 
-   use_system_physfs = ('glpk' not in get_option('force_fallback_for') and 'forcefallback' != get_option('wrap_mode'))
+   use_system_physfs = ('physfs' not in get_option('force_fallback_for') and 'forcefallback' != get_option('wrap_mode'))
    if use_system_physfs
       system_physfs = dependency('physfs', required: false)
       if not system_physfs.found()