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>