[gobject-introspection] MSVC builds: Use a envvar for pkg-config

[Chun-wei Fan <fanchunwei src gnome org>]

commit f5565ba632cf78ca2bd4b538eac1bf0cb8b393bd
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Mon Apr 11 11:11:40 2016 +0800

    MSVC builds: Use a envvar for pkg-config
    
    Allow using a envvar to specify the path to pkg-config, as it may not be
    in the PATH.
    
    Suggestion given by the HexChat project.

 build/win32/introspection-msvc.mak |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/build/win32/introspection-msvc.mak b/build/win32/introspection-msvc.mak
index f6fff49..8739844 100644
--- a/build/win32/introspection-msvc.mak
+++ b/build/win32/introspection-msvc.mak
@@ -37,6 +37,11 @@ PKG_CONFIG_PATH=$(PREFIX_FULL)\lib\pkgconfig;$(PKG_CONFIG_PATH)
 PYTHON=python
 !endif
 
+# Path to the pkg-config tool, if not already in the PATH
+!if "$(PKG_CONFIG)" == ""
+PKG_CONFIG=pkg-config
+!endif
+
 # Don't change anything following this line!
 
 GIR_SUBDIR = share\gir-1.0
@@ -56,7 +61,7 @@ ERROR_MSG =
 BUILD_INTROSPECTION = TRUE
 
 !if ![set PKG_CONFIG_PATH=$(PKG_CONFIG_PATH)]  \
-       && ![pkg-config --print-errors --errors-to-stdout $(CHECK_PACKAGE) > pkgconfig.x]       \
+       && ![$(PKG_CONFIG) --print-errors --errors-to-stdout $(CHECK_PACKAGE) > pkgconfig.x]    \
        && ![setlocal]  \
        && ![set file="pkgconfig.x"]    \
        && ![FOR %A IN (%file%) DO @echo PKG_CHECK_SIZE=%~zA > pkgconfig.chksize]       \