[gdb/testsuite] Add target board cc-with-gnu-debuglink.exp

Add target board cc-with-gnu-debuglink.exp that splits off debuginfo into a
seperate .debug file and links to it using .gnu_debuglink.

Tested on x86_64-linux.

gdb/ChangeLog:

2021-05-21  Tom de Vries  <tdevries@suse.de>

	PR testsuite/25047
	* contrib/cc-with-tweaks.sh: Handle -l.

gdb/testsuite/ChangeLog:

2021-05-21  Tom de Vries  <tdevries@suse.de>

	PR testsuite/25047
	* boards/cc-with-gnu-debuglink.exp: New file.