Make OSX builds default to Clang for compilation.

The GCC included in current versions of Xcode is quite old and has a
number of bugs that make it difficult to use for building BSL. Since
Xcode includes Clang and that is the supported compiler for the OSX
environment (and is used when the build is performed by xcodebuild),
this patch changes the build system to use Clang on OSX instead of GCC
for Makefile-driven builds. Users can still override this behavior if
they wish by specifying "CC=gcc CXX=g++" on the 'make' command line.
Add JUnit-style output format to run_unit_tests.py.

This patch adds a new output format to the test driver execution script,
which captures test case output, collects results and emits them in a
form that other tools can consume. This mode is enabled by specifying
"--junit=<file.xml>" to the script.
Add support for 'ldflags_extra' in build system.

This patch adds the ability to specify extra (additional) flags to the
linker when bsl_gyp.py is executed (by adding a command line option
similar to '-D ldflags_extra=<flags>'). This parallels the existing
'cflags_extra' support.
Eliminate reliance on special CLANG_GNUC_* macros.

The BSL platform header relied on custom preprocessor macros that had
to be provided by the build system when Clang was used to compile. These
have been replaced with hardcoded values that configure the code to act
as if Clang was GCC 4.4.0.
Disable inlining for 'Debug' builds on GCC-type compilers.

Inlining interferes with debugging and also interferes with code
coverage analysis, so this patch disables it for Debug builds
when GCC or a compatible compiler is being used.
Import BSL-QC continuous integration job script.
Correct some script errors.
Run lcov 'gather' step serially to avoid failures.
Add some copyright/license headers.
Disable profile/code coverage until tools are merged.
Import internal commit de0473a297248668b55a3385ba5eda7b73184ff3 : [APPROVAL] pending/master/restore_non_standard_bsl_hash_for_strings_drqs37540921 to master
Import internal commit 49a9b029b9417d6b4bfe8ff366c554d82e4fb7d8 : [APPROVAL] pending/master/bslalg_autoarray-move-destructor-usage-drqs-34554786 to master
Merge branch 'import' into import-test
Re-generate gyp files
Merge branch 'upstream-master' into import-test
Increase timeout to see how long bsl_hashtable.t takes to complete
Adding Travis-CI config.
Fixing bde_gyp.py invocation.
Restrict Travis-CI to gcc.