Handle CRLF when reading XML on Windows

xml-support.c uses FOPEN_RT, but then reads the entire contents of the
file and verifies that the number of bytes read matches the length.
This can fail on Windows, where the read will translate line
terminators.

This patch fixes the bug by changing xml-support.c to use FOPEN_RB.
This works because expat correctly handles \r\n line terminators.

gdb/ChangeLog
2019-12-11  Tom Tromey  <tromey@adacore.com>

	* xml-support.c (xml_fetch_content_from_file): Use FOPEN_RB.

gdb/testsuite/ChangeLog
2019-12-11  Tom Tromey  <tromey@adacore.com>

	* gdb.xml/tdesc-arch.exp (set_arch): Add "trans_mode" parameter.
	Add crlf test.

Change-Id: I548438f33eed284dde1de8babf755eaa1a40319d