build: use pkg-config (if available) to configure libpcre

Problem reported by Mike Frysinger in: http://bugs.gnu.org/16757
* bootstrap.conf (bootstrap_post_import_hook):
Copy pkg-config's pkg.m4.
* configure.ac: Invoke PKG_PROG_PKG_CONFIG.
* m4/pcre.m4 (gl_FUNC_PCRE): Rewrite to use pkg-config if
available, and to test that pcre_compile can be linked to.
* src/Makefile.am (AM_CFLAGS): Add PCRE_CFLAGS.
(grep_LDADD): Add PCRE_LIBS.
* src/pcresearch.c: Simply include <pcre.h> if HAVE_LIBPCRE,
since 'configure' arranges for the appropriate -I option now.

1 files changed, 39 insertions, 23 deletions

diff --git a/m4/pcre.m4 b/m4/pcre.m4
index 99c7446c..ccb9dbc4 100644
--- a/m4/pcre.m4
+++ b/m4/pcre.m4
@@ -1,5 +1,4 @@
 # pcre.m4 - check for libpcre support
-# serial 1
 
 # Copyright (C) 2010-2015 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
@@ -17,32 +16,49 @@ AC_DEFUN([gl_FUNC_PCRE],
      esac],
     [test_pcre=yes])
 
-  LIB_PCRE=
-  AC_SUBST([LIB_PCRE])
+  PCRE_CFLAGS=
+  PCRE_LIBS=
+  AC_SUBST([PCRE_CFLAGS])
+  AC_SUBST([PCRE_LIBS])
   use_pcre=no
 
-  if test x"$test_pcre" = x"yes"; then
-    AC_CHECK_HEADERS([pcre.h])
-    AC_CHECK_HEADERS([pcre/pcre.h])
-    if test $ac_cv_header_pcre_h = yes \
-        || test $ac_cv_header_pcre_pcre_h = yes; then
-      pcre_saved_LIBS=$LIBS
-      AC_SEARCH_LIBS([pcre_compile], [pcre],
-        [test "$ac_cv_search_pcre_compile" = "none required" ||
-         LIB_PCRE=$ac_cv_search_pcre_compile])
-      AC_CHECK_FUNCS([pcre_compile])
-      LIBS=$pcre_saved_LIBS
-      if test $ac_cv_func_pcre_compile = yes; then
-        use_pcre=yes
-      fi
-    fi
-    if test $use_pcre = no; then
-      AC_MSG_WARN([libpcre development library was not found or not usable.])
+  if test $test_pcre = yes; then
+    PKG_CHECK_MODULES([PCRE], [libpcre], [],
+      [if test -r /usr/include/pcre/pcre.h &&
+          test ! -r /usr/include/pcre.h
+       then
+         PCRE_CFLAGS=-I/usr/include/libpng
+       fi
+       PCRE_LIBS=-lpcre])
+
+    AC_CACHE_CHECK([for pcre_compile], [pcre_cv_have_pcre_compile],
+      [pcre_saved_CFLAGS=$CFLAGS
+       pcre_saved_LIBS=$LIBS
+       CFLAGS="$CFLAGS $PCRE_CFLAGS"
+       LIBS="$PCRE_LIBS $LIBS"
+       AC_LINK_IFELSE(
+         [AC_LANG_PROGRAM([[#include <pcre.h>
+                          ]],
+            [[pcre *p = pcre_compile (0, 0, 0, 0, 0);
+              return !p;]])],
+         [pcre_cv_have_pcre_compile=yes],
+         [pcre_cv_have_pcre_compile=no])
+       CFLAGS=$pcre_saved_CFLAGS
+       LIBS=$pcre_saved_LIBS])
+
+    if test "$pcre_cv_have_pcre_compile" = yes; then
+      use_pcre=yes
+    else
       AC_MSG_WARN([AC_PACKAGE_NAME will be built without pcre support.])
     fi
   fi
 
-  AC_DEFINE_UNQUOTED([HAVE_LIBPCRE], [`test $use_pcre != yes; echo $?`],
-    [Define to 1 if you have the Perl Compatible Regular Expressions
-     library (-lpcre).])
+  if test $use_pcre = yes; then
+    AC_DEFINE([HAVE_LIBPCRE], [1],
+      [Define to 1 if you have the Perl Compatible Regular Expressions
+       library (-lpcre).])
+  else
+    PCRE_CFLAGS=
+    PCRE_LIBS=
+  fi
 ])