Disable styling when running in batch mode

The GCC Guality testsuite within GCC compiles C/C++ files in GCC at
various optimization levels then debugs them in GDB, checking that
program values can be read.  This is done within the dejagnu framework.

The new style options in GDB have broken many of the tests due to the
testsuite being unable to process the new control characters.  The fix
in Guality is to either to improve the string matching or to disable
styling on the cli or init file (after checking gdb is recent enough
to support styling).

This fix will also need making an any other testsuites in the wild
that use GDB.

An alternative would be to automatically disable styling when using GDB
in batch mode.  The reasoning here is that batch mode is only used when
automating GDB and any output will be processed later either with text
processing tools or viewed in text editors, many of these will not
correctly handle the control characters by default.  This ensures GDB
continues to work as expected.  Anyone who explicitly wants styling in
batch mode can enable it either in the init file or adding to the batch
file - but that would not be the standard use case.

Patch simply disables style after reading the batch command flag, before
reading in the init file or batch file.

gdb/ChangeLog:

	* main.c (captured_main_1): Disable styling in batch mode.