Add missing qRegisterInfo option to gdbremote testcase

[fjricci]

Summary

"gcc" is equivalent to "ehframe" in ProcessGDBRemote, but
only "ehframe" was a valid response in the test suite.

I know that "gcc" was replaced by "ehframe" in the test suite in D247741,
but since it hasn't been removed from ProcessGDBRemote, I'm
assuming that it's still a valid parameter.

[jasonmolenda]

Yes, good idea to add that. ProcessGDBRemote will need to accept "gcc" for at least a few years while old debugservers etc are floating around.

lldb/trunk/packages/Python/lldbsuite/test/tools/lldb-server/gdbremote_testcase.py

class GdbRemoteTestCaseBase(TestBase):
     _KNOWN_REGINFO_KEYS = [
         "name",
         "alt-name",
         "bitsize",
         "offset",
         "encoding",
         "format",
         "set",
+        "gcc",
         "ehframe",
         "dwarf",
         "generic",
         "container-regs",
         "invalidate-regs"
     ]
 
     def assert_valid_reg_info(self, reg_info):