[lldb] [lldbtest] Fix getBuildFlags() not to use libstdc++ on NetBSD

Remove the code forcing -stdlib=libstdc++ on NetBSD in getBuildFlags()
method.  NetBSD uses libc++ everywhere else, and using libstdc++ here
causes lang/cpp/dynamic-value to fail to build.

Differential Revision: https://reviews.llvm.org/D58871

llvm-svn: 355273

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -1666,7 +1666,8 @@ class Base(unittest2.TestCase):
         elif self.getPlatform() == "openbsd":
             cflags += " -stdlib=libc++"
         elif self.getPlatform() == "netbsd":
-            cflags += " -stdlib=libstdc++"
+            # NetBSD defaults to libc++
+            pass
         elif "clang" in self.getCompiler():
             cflags += " -stdlib=libstdc++"