gdb/testsuite: Remove duplicates from gdb.base/funcargs.exp
When running the testsuite, I have:
Running .../gdb/testsuite/gdb.base/funcargs.exp ...
DUPLICATE: gdb.base/funcargs.exp: run to call2a
Fix by using proc_with_prefix instead on plain proc to create logical
function blocks.
Tested on x86_64-linux.