build,meson: fix 'export_packages' in GIR setup

The 'export_packages' field in the generate_gir() command should
include the name of the pkg-config package being exported, not the
name of the library file.

Without this change, building GIR files depending on the one we
provide here would fail as the corresponding .pc file isn't found.

libmm-glib/meson.build

@@ -127,8 +127,10 @@ sources = files(
 
 deps = [include_dep]
 
+libname = 'mm-glib'
+
 libmm_glib = shared_library(
-  'mm-glib',
+  libname,
   version: mm_glib_version,
   sources: sources,
   include_directories: top_inc,
@@ -147,7 +149,7 @@ libmm_glib_dep = declare_dependency(
 pkg.generate(
   libraries: libmm_glib,
   version: mm_version,
-  name: 'mm-glib',
+  name: libname,
   description: 'Library to control and monitor the ModemManager',
   subdirs: mm_glib_name,
   # FIXME: produced by the inhability of meson to use internal dependencies
@@ -180,7 +182,7 @@ if enable_gir
     symbol_prefix: gir_prefix.to_lower(),
     extra_args: args,
     header: 'libmm-glib.h',
-    export_packages: gir_ns,
+    export_packages: libname,
     install: true,
   )