configure, tests/tcg: simplify GDB conditionals

Unify HAVE_GDB_BIN (currently in config-host.mak) and
HOST_GDB_SUPPORTS_ARCH into a single GDB variable in
config-target.mak.

Reviewed-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

meson.build

@@ -4021,8 +4021,8 @@ summary(summary_info, bool_yn: true, section: 'Directories')
 summary_info = {}
 summary_info += {'python':            '@0@ (version: @1@)'.format(python.full_path(), python.language_version())}
 summary_info += {'sphinx-build':      sphinx_build}
-if config_host.has_key('HAVE_GDB_BIN')
-  summary_info += {'gdb':             config_host['HAVE_GDB_BIN']}
+if config_host.has_key('GDB')
+  summary_info += {'gdb':             config_host['GDB']}
 endif
 summary_info += {'iasl':              iasl}
 summary_info += {'genisoimage':       config_host['GENISOIMAGE']}