Using '\r' instead of '\015' for MSYS2/mingw

Hi,

Current MSYS2/mingw sed appears not to handle '\015'.
This causes failure below.
======================================================================
checking command to parse /mingw64/bin/nm -B output from gcc object... failed
======================================================================

This patch fixes this issue with using '\r' instead of  '\015', and
this affects only mingw.

I originally posted this issue to MSYS2 users ML.
https://sourceforge.net/p/msys2/mailman/message/35675002/

Best regards,

Kinichiro Inoguchi

diff --git a/m4/libtool.m4 b/m4/libtool.m4
index ee292af..01d7860 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -4018,7 +4018,7 @@ $lt_c_name_lib_hook\
 opt_cr=
 case $build_os in
 mingw*)
-  opt_cr=`$ECHO 'x\{0,1\}' | tr x '\015'` # option cr in regexp
+  opt_cr='\r\{0,1\}' # option cr in regexp
   ;;
 esac