configure: re-purpose the tcg test compiler configs for vdso building

All the tcg tests are in meson now so there is no reason to put the
config-target.mak files in those directories. We also don't need the
GDB feature tests or to emit prerequsistes.

The vdso re-build blob does use the compiler definitions though so
we can emit the details for that and tweak the vdso makefiles to point
at the right place. Note some of the vdso makefiles build both 32 and
64 bit versions from the same compiler.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Tested-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20260917165602.3405537-5-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>