Add new gdb.ada/bp_c_mixed_case testcase for PR gdb/22670
    
    This patch adds a new testcase to demonstrate a regression introduced by:
    
        commit b5ec771e60c1a0863e51eb491c85c674097e9e13
        Date:   Wed Nov 8 14:22:32 2017 +0000
        Subject: Introduce lookup_name_info and generalize Ada's FULL/WILD name matching
    
    The purpose of the testcase is to verify that a user can insert
    a breakpoint on a C function while debugging Ada, even if the name
    of the function includes uppercase letters, requiring us to use
    Ada's "<...>" notation to tell the GDB that the symbol name should
    be looked up verbatim.
    
    As of the commit above, GDB is no longer finding the function:
    
        (gdb) break <MixedCaseFunc>
        Function "<MixedCaseFunc>" not defined.
        Make breakpoint pending on future shared library load? (y or [n])
    
    Before the patch, the breakpoint was inserted without problem.
    
    gdb/testsuite/ChangeLog:
    
            PR gdb/22670
            * gdb.ada/bp_c_mixed_case: New testcase.
    
    Tested on x86_64-linux; generates a KPASS before the regression
    was introduced, and now generates a KFAIL.