Honor the --with-${library}=path for AST_EXT_TOOL_CHECK

(closes issue #16991)
Reported by: pprindeville
Patches: 
      with_netsnmp.patch.txt uploaded by twilson (license 396)
Tested by: twilson

Review: https://reviewboard.asterisk.org/r/739/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@272254 65c4cc65-6c06-0410-ace0-fbb531ad65f3

autoconf/ast_ext_tool_check.m4

@@ -7,7 +7,7 @@ AC_DEFUN([AST_EXT_TOOL_CHECK],
 [
     if test "x${PBX_$1}" != "x1" -a "${USE_$1}" != "no"; then
 	PBX_$1=0
-	AC_CHECK_TOOL(CONFIG_$1, $2, No)
+	AC_PATH_TOOL(CONFIG_$1, $2, No, [${$1_DIR}/bin:$PATH])
 	if test ! "x${CONFIG_$1}" = xNo; then
 	    if test x"$3" = x ; then A=--cflags ; else A="$3" ; fi
 	    $1_INCLUDE=$(${CONFIG_$1} $A)