m4macros: Allow information from pkg-config to be overridden

By using PKG_CHECK_VAR, we declare $GLIB_COMPILE_SCHEMAS,
$GLIB_GENMARSHAL, $GOBJECT_QUERY, $GLIB_MKENUMS and
$GLIB_COMPILE_RESOURCES as Autoconf "precious variables" with AC_ARG_VAR,
similar to $PKG_CONFIG and $CC, so that they can be put on a configure
command line:

    ./configure GLIB_COMPILE_RESOURCES=my-glib-compile-resources

If they are set to a non-empty value, PKG_CHECK_VAR will use that
instead of auto-detecting from pkg-config, so that builders can
override them, for example when cross-compiling.

Similarly, use the standard PKG_CHECK_MODULES macro to get GLib's CFLAGS
and LIBS.

It's possible that most of the rest of each macro can also disappear,
but for the moment I've given them the benefit of the doubt.

This does result in printing "checking for GLIB" twice (once for
PKG_CHECK_MODULES and once for GLib's custom checks), but if you're
using Autotools, you probably don't have a strong objection to overly
verbose output.

Signed-off-by: Simon McVittie <smcv@collabora.com>

m4macros/glib-2.0.m4

@@ -2,7 +2,7 @@
 # Owen Taylor     1997-2001
 
 # Increment this whenever this file is changed.
-#serial 1
+#serial 2
 
 dnl AM_PATH_GLIB_2_0([MINIMUM-VERSION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND [, MODULES]]]])
 dnl Test for GLIB, and define GLIB_CFLAGS and GLIB_LIBS, if gmodule, gobject,
@@ -12,10 +12,16 @@ AC_DEFUN([AM_PATH_GLIB_2_0],
 [dnl 
 dnl Get the cflags and libraries from pkg-config
 dnl
+
+dnl We can't use PKG_PREREQ because that needs 0.29.
+m4_ifndef([PKG_PROG_PKG_CONFIG],
+          [pkg.m4 version 0.28 or later is required])
+
 AC_ARG_ENABLE(glibtest, [  --disable-glibtest      do not try to compile and run a test GLIB program],
 		    , enable_glibtest=yes)
 
-  pkg_config_args=glib-2.0
+  min_glib_version=ifelse([$1], [], [2.0.0], [$1])
+  pkg_config_args="glib-2.0 >= $min_glib_version"
   for module in . $4
   do
       case "$module" in
@@ -46,7 +52,15 @@ AC_ARG_ENABLE(glibtest, [  --disable-glibtest      do not try to compile and run
     PKG_CONFIG=no
   fi
 
-  min_glib_version=ifelse([$1], ,2.0.0,$1)
+  dnl For GLIB_CFLAGS and GLIB_LIBS
+  PKG_CHECK_MODULES([GLIB], [$pkg_config_args >= $min_glib_version], [:], [:])
+
+  dnl For the tools
+  PKG_CHECK_VAR([GLIB_GENMARSHAL], [glib-2.0], [glib_genmarshal])
+  PKG_CHECK_VAR([GOBJECT_QUERY], [glib-2.0], [gobject_query])
+  PKG_CHECK_VAR([GLIB_MKENUMS], [glib-2.0], [glib_mkenums])
+  PKG_CHECK_VAR([GLIB_COMPILE_RESOURCES], [gio-2.0], [glib_compile_resources])
+
   AC_MSG_CHECKING(for GLIB - version >= $min_glib_version)
 
   if test x$PKG_CONFIG != xno ; then
@@ -64,13 +78,6 @@ AC_ARG_ENABLE(glibtest, [  --disable-glibtest      do not try to compile and run
   fi
 
   if test x"$no_glib" = x ; then
-    GLIB_GENMARSHAL=`$PKG_CONFIG --variable=glib_genmarshal glib-2.0`
-    GOBJECT_QUERY=`$PKG_CONFIG --variable=gobject_query glib-2.0`
-    GLIB_MKENUMS=`$PKG_CONFIG --variable=glib_mkenums glib-2.0`
-    GLIB_COMPILE_RESOURCES=`$PKG_CONFIG --variable=glib_compile_resources gio-2.0`
-
-    GLIB_CFLAGS=`$PKG_CONFIG --cflags $pkg_config_args`
-    GLIB_LIBS=`$PKG_CONFIG --libs $pkg_config_args`
     glib_config_major_version=`$PKG_CONFIG --modversion glib-2.0 | \
            sed 's/\([[0-9]]*\).\([[0-9]]*\).\([[0-9]]*\)/\1/'`
     glib_config_minor_version=`$PKG_CONFIG --modversion glib-2.0 | \
@@ -204,11 +211,5 @@ main (void)
      GLIB_COMPILE_RESOURCES=""
      ifelse([$3], , :, [$3])
   fi
-  AC_SUBST(GLIB_CFLAGS)
-  AC_SUBST(GLIB_LIBS)
-  AC_SUBST(GLIB_GENMARSHAL)
-  AC_SUBST(GOBJECT_QUERY)
-  AC_SUBST(GLIB_MKENUMS)
-  AC_SUBST(GLIB_COMPILE_RESOURCES)
   rm -f conf.glibtest
 ])

m4macros/gsettings.m4

@@ -1,5 +1,5 @@
 # Increment this whenever this file is changed.
-#serial 1
+#serial 2
 
 dnl GLIB_GSETTINGS
 dnl Defines GSETTINGS_SCHEMAS_INSTALL which controls whether
@@ -8,6 +8,10 @@ dnl
 
 AC_DEFUN([GLIB_GSETTINGS],
 [
+  dnl We can't use PKG_PREREQ because that needs 0.29.
+  m4_ifndef([PKG_PROG_PKG_CONFIG],
+            [pkg.m4 version 0.28 or later is required])
+
   m4_pattern_allow([AM_V_GEN])
   AC_ARG_ENABLE(schemas-compile,
                 AS_HELP_STRING([--disable-schemas-compile],
@@ -20,11 +24,9 @@ AC_DEFUN([GLIB_GSETTINGS],
   AC_SUBST([GSETTINGS_DISABLE_SCHEMAS_COMPILE])
   PKG_PROG_PKG_CONFIG([0.16])
   AC_SUBST(gsettingsschemadir, [${datadir}/glib-2.0/schemas])
-  if test x$cross_compiling != xyes; then
+  AS_IF([test x$cross_compiling != xyes],
-    GLIB_COMPILE_SCHEMAS=`$PKG_CONFIG --variable glib_compile_schemas gio-2.0`
+        [PKG_CHECK_VAR([GLIB_COMPILE_SCHEMAS], [gio-2.0], [glib_compile_schemas])],
-  else
+        [AC_PATH_PROG([GLIB_COMPILE_SCHEMAS], [glib-compile-schemas])])
-    AC_PATH_PROG(GLIB_COMPILE_SCHEMAS, glib-compile-schemas)
-  fi
   AC_SUBST(GLIB_COMPILE_SCHEMAS)
   if test "x$GLIB_COMPILE_SCHEMAS" = "x"; then
     ifelse([$2],,[AC_MSG_ERROR([glib-compile-schemas not found.])],[$2])