gdb, gdbsupport: configure: factor out yes/no/auto value checking

gdb, gdbsupport: configure: factor out yes/no/auto value checking

Factor out the code that checks that a value is yes/no or yes/no/auto.
Add two macros to gdbsupport/common.m4 and use them in gdb/configure.ac

I inspected the changes to configure.  Other than whitespace changes, we
have some benign changes to the error messages (one of them had an error
actually).  There are changes to the --enable-source-highlight and
--enable-libbacktrace handling, but setting enable_source_highlight /
enable_libbacktrace was not really useful anyway, they already had the
right value.

Change-Id: I92587aec36874309e1605e2d60244649f09a757a