Consistently quote variables used with "test"

Consistently quote variables used with "test"

This ensures that empty variables and variables with spaces are handled
correctly.

Code was inconsistent on whether the constant string (e.g. yes/no)
should also be quoted; I tried to be consistent with surrounding code.

This fixes the error Eli reported during configure with mingw (though that
was not fatal).

gdb/ChangeLog:

2019-12-19  Christian Biesinger  <cbiesinger@google.com>

	* configure: Regenerate.
	* configure.ac: Quote variable arguments of test.
	* gdbsupport/common.m4: Likewise.

gdb/gdbserver/ChangeLog:

2019-12-19  Christian Biesinger  <cbiesinger@google.com>

	* configure: Regenerate.
	* configure.ac: Quote variable arguments of test.

Change-Id: I220e78b52c7db88b9dd058eda604635b03464fac