configure: Remove carriage return ('\r') in Windows CC_IDENT

Currently the Windows CC_IDENT is ended with '\r\n'. "head -n1" will not
remove the '\r' and this is causing building error in Chromium.

This CL adds "tr -d '\r'" to remove '\r' in the CC_IDENT string. Since in
most cases '\r' only appears at the end of a string/line, this should
work in most cases.

See example:

printf "hello\r\nworld\r\n" | head -n1 | hd
00000000  68 65 6c 6c 6f 0d 0a                              |hello..|

printf "hello\r\nworld\r\n" | head -n1 | tr -d '\r' | hd
00000000  68 65 6c 6c 6f 0a                                 |hello.|

Also note a similar previous change at:
https://lists.ffmpeg.org/pipermail/ffmpeg-cvslog/2013-October/069950.html

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

configure

@@ -4289,7 +4289,7 @@ probe_cc(){
         _ld_path='-libpath:'
     elif $_cc -nologo- 2>&1 | grep -q Microsoft; then
         _type=msvc
-        _ident=$($_cc 2>&1 | head -n1)
+        _ident=$($_cc 2>&1 | head -n1 | tr -d '\r')
         _DEPCMD='$(DEP$(1)) $(DEP$(1)FLAGS) $($(1)DEP_FLAGS) $< 2>&1 | awk '\''/including/ { sub(/^.*file: */, ""); gsub(/\\/, "/"); if (!match($$0, / /)) print "$@:", $$0 }'\'' > $(@:.o=.d)'
         _DEPFLAGS='$(CPPFLAGS) $(CFLAGS) -showIncludes -Zs'
         _cflags_speed="-O2"