use autoconf macro to check for pkg-config (closes #15506)

Misc/NEWS

@@ -238,6 +238,9 @@ Tests
 Build
 -----
 
+- Issue #15506: Use standard PKG_PROG_PKG_CONFIG autoconf macro in the configure
+  script.
+
 - Issue #22935: Allow the ssl module to be compiled if openssl doesn't support
   SSL 3.
 

configure

@@ -650,6 +650,8 @@ USE_SIGNAL_MODULE
 TCLTK_LIBS
 TCLTK_INCLUDES
 LIBFFI_INCLUDEDIR
+PKG_CONFIG_LIBDIR
+PKG_CONFIG_PATH
 PKG_CONFIG
 SHLIBS
 CFLAGSFORSHARED
@@ -828,7 +830,10 @@ CFLAGS
 LDFLAGS
 LIBS
 CPPFLAGS
-CPP'
+CPP
+PKG_CONFIG
+PKG_CONFIG_PATH
+PKG_CONFIG_LIBDIR'
 
 
 # Initialize some variables set by options.
@@ -1514,6 +1519,11 @@ Some influential environment variables:
   CPPFLAGS    (Objective) C/C++ preprocessor flags, e.g. -I<include dir> if
               you have headers in a nonstandard directory <include dir>
   CPP         C preprocessor
+  PKG_CONFIG  path to pkg-config utility
+  PKG_CONFIG_PATH
+              directories to add to pkg-config's search path
+  PKG_CONFIG_LIBDIR
+              path overriding pkg-config's built-in search path
 
 Use these variables to override the choices made by `configure' or to help
 it to find libraries and programs with nonstandard names/locations.
@@ -9218,7 +9228,15 @@ $as_echo "no" >&6; }
 fi
 
 
-if test -n "$ac_tool_prefix"; then
+
+
+
+
+
+
+
+if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
+	if test -n "$ac_tool_prefix"; then
   # Extract the first word of "${ac_tool_prefix}pkg-config", so it can be a program name with args.
 set dummy ${ac_tool_prefix}pkg-config; ac_word=$2
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
@@ -9316,6 +9334,20 @@ else
   PKG_CONFIG="$ac_cv_path_PKG_CONFIG"
 fi
 
+fi
+if test -n "$PKG_CONFIG"; then
+	_pkg_min_version=0.9.0
+	{ $as_echo "$as_me:${as_lineno-$LINENO}: checking pkg-config is at least version $_pkg_min_version" >&5
+$as_echo_n "checking pkg-config is at least version $_pkg_min_version... " >&6; }
+	if $PKG_CONFIG --atleast-pkgconfig-version $_pkg_min_version; then
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; }
+	else
+		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+		PKG_CONFIG=""
+	fi
+fi
 
 # Check for use of the system expat library
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-system-expat" >&5

configure.ac

@@ -2335,7 +2335,7 @@ LIBS="$withval $LIBS"
 ],
 [AC_MSG_RESULT(no)])
 
-AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
+PKG_PROG_PKG_CONFIG
 
 # Check for use of the system expat library
 AC_MSG_CHECKING(for --with-system-expat)