Reset LIBS temporarily to make sure PHP_CHECK_FUNC will look into libc.

See Gentoo bug #364139. https://bugs.gentoo.org/show_bug.cgi?id=364139
Reported by Naohiro Aota.

NEWS

@@ -3,6 +3,11 @@ PHP                                                                        NEWS
 ?? ??? 2012, PHP 5.3.12
 
 ?? ??? 2012, PHP 5.3.11
+- Iconv extension:
+  . Fixed a bug that iconv extension fails to link to the correct library
+    when another extension makes use of a library that links to the iconv
+    library. See https://bugs.gentoo.org/show_bug.cgi?id=364139 for detail.
+    (Moriyoshi)
 
 (merge after 5.3.11 release)
 

acinclude.m4

@@ -2438,7 +2438,12 @@ AC_DEFUN([PHP_SETUP_ICONV], [
   dnl
   dnl Check libc first if no path is provided in --with-iconv
   dnl
+
   if test "$PHP_ICONV" = "yes"; then
+    dnl Reset LIBS temporarily as it may have already been included
+    dnl -liconv in.
+    LIBS_save="$LIBS"
+    LIBS=
     AC_CHECK_FUNC(iconv, [
       found_iconv=yes
     ],[
@@ -2448,6 +2453,7 @@ AC_DEFUN([PHP_SETUP_ICONV], [
         found_iconv=yes
       ])
     ])
+    LIBS="$LIBS_save"
   fi
 
   dnl