[geary] Use PKG_CONFIG_EXECUTABLE provided by find_package(PkgConfig)

[Michael Gratton <mjog src gnome org>]

commit 7166c15ea3a46a034d7bb3bf7cc9d6d11842950a
Author: Heiko Becker <heirecka exherbo org>
Date:   Tue Oct 6 19:50:21 2015 +0200

    Use PKG_CONFIG_EXECUTABLE provided by find_package(PkgConfig)
    
    find_package(PkgConfig} respects the PKG_CONFIG environment variable
    when trying to find pkg-config. This is helpful with a differently
    named pkg-config executable, for example an arch-prefixed one.

 cmake/GSettings.cmake |    2 +-
 src/CMakeLists.txt    |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/cmake/GSettings.cmake b/cmake/GSettings.cmake
index df32e4f..1438fd5 100644
--- a/cmake/GSettings.cmake
+++ b/cmake/GSettings.cmake
@@ -18,7 +18,7 @@ if (GSETTINGS_COMPILE_IN_PLACE)
 endif ()
 
 macro(add_schemas GSETTINGS_TARGET SCHEMA_DIRECTORY PREFIX)
-    set(PKG_CONFIG_EXECUTABLE pkg-config)
+    find_package(PkgConfig)
     
     # Locate all schema files.
     file(GLOB all_schema_files
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 8bd572a..0f1e7a1 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -602,7 +602,7 @@ add_custom_command(
     WORKING_DIRECTORY
         ${CMAKE_SOURCE_DIR}/bindings/metadata
     COMMAND
-        vapigen --pkg=gio-2.0 --pkg=gtk+-3.0 --pkg=libsoup-2.4 --metadatadir=. 
--metadatadir=${WEBKITGTK_METADATA_DIR} --library=webkitgtk-3.0 --directory=${CMAKE_BINARY_DIR}/src 
${WEBKITGTK_CUSTOM_VALA} `pkg-config --variable=girdir gobject-introspection-1.0`/WebKit-3.0.gir
+        vapigen --pkg=gio-2.0 --pkg=gtk+-3.0 --pkg=libsoup-2.4 --metadatadir=. 
--metadatadir=${WEBKITGTK_METADATA_DIR} --library=webkitgtk-3.0 --directory=${CMAKE_BINARY_DIR}/src 
${WEBKITGTK_CUSTOM_VALA} `${PKG_CONFIG_EXECUTABLE} --variable=girdir gobject-introspection-1.0`/WebKit-3.0.gir
 )
 
 # Geary client app