The local board file ensures that the sysroot is always set to load
files from the local filesystem.
Add a gdbserver test to explicitly test the sysroot set to both the
remote target and the local filesystem.
gdb/testsuite/ChangeLog:
* gdb.server/sysroot.c: New test.
* gdb.server/sysroot.exp: New file.
* lib/gdbserver-support.exp (gdb_target_cmd): Add additional text
matching param.