libassuan: don't search for gpgrt-config on build host

libassuan: don't search for gpgrt-config on build host

When another project uses the libassuan.m4 file to find libassuan details,
the macro first tries to execute the gpgrt-config executable if it can find
any in the PATH. However it also prepends the PATH with ${prefix}/bin, which
usually translates to /usr/bin - in case the build host has this executable
installed, then it is executed, and it shows warnings about mis-matched
architecture before pkg-config would be executed.

To avoid this, extend the existing patch to not prepend the PATH with the
build host path - the existing PATH should be good enough.

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>
Cc: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>