Enable TestDataFormatterStdMap on linux (libstdc++) with clang.

Summary:
This test should have been enabled along with
7181dae1248cc1b03505cca1b7c6e3dfeffefc0a, but since the test was
actually crashing, I thought it was a much deeper problem. Turns out,
all I had to do was to add "-fno-limit-debug-info" when compiling
the test case.

The test is still skipped when the testcase is compiled with GCC.

Test Plan: dotest.py -p TestDataFormatterStdMap

Reviewers: vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8364

llvm-svn: 232432