[gobject-introspection] meson: use pkg-config directly for libffi cflags and libs

[Christoph Reiter <creiter src gnome org>]

commit c296d4c47fda2e25b1a9aa76382b34ebd1c0c453
Author: Aaron Boxer <aaron boxer collabora com>
Date:   Mon Jul 22 21:22:16 2019 -0600

    meson: use pkg-config directly for libffi cflags and libs
    
    meson 0.50.1 pkg-config API can't introspect clfags and libs, so we need
    to run pkg-config itself to get these

 meson.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index 941d63ec..0a123e14 100644
--- a/meson.build
+++ b/meson.build
@@ -193,8 +193,9 @@ endif
 pkgconfig_conf.set('VERSION', meson.project_version())
 pkgconfig_conf.set('FFI_PC_PACKAGES', 'libffi')
 if libffi_dep.type_name() == 'pkgconfig'
-  pkgconfig_conf.set('FFI_PC_CFLAGS', libffi_dep.get_pkgconfig_variable('Cflags'))
-  pkgconfig_conf.set('FFI_PC_LIBS', libffi_dep.get_pkgconfig_variable('Libs'))
+  prog_pkgconfig = find_program('pkg-config')
+  pkgconfig_conf.set('FFI_PC_CFLAGS', run_command(prog_pkgconfig, ['libffi', '--cflags-only-I']).stdout())
+  pkgconfig_conf.set('FFI_PC_LIBS', run_command(prog_pkgconfig, ['libffi', '--libs-only-l']).stdout())
 else
   # XXX: We can't know the correct values for these, needs meson API. Maybe we
   # should use meson's pkgconfig module to generate the whole file.