Bump up minimum supported clang to 4.0

tools/dockerfile/test/cxx_ubuntu1604_x64/Dockerfile

@@ -82,10 +82,8 @@ RUN apt-get update && apt-get install -y cmake && apt-get clean
 RUN mkdir /var/local/jenkins
 
 
-# The clang-3.6 symlink for the default clang version was added
-# to Ubuntu 16.04 recently, so make sure it's installed.
-# Also install clang3.7.
-RUN apt-get update && apt-get -y install clang-3.6 clang-3.7 && apt-get clean
+# Installs clang 4.0 and 5.0, the clang++ is included in clang pcakges
+RUN apt-get update && apt-get -y install clang-4.0 clang-5.0 && apt-get clean
 
 # Define the default command.
 CMD ["bash"]

tools/run_tests/run_tests.py

@@ -487,14 +487,14 @@ class CLanguage(object):
             return ('buster', [])
         elif compiler == 'gcc_musl':
             return ('alpine', [])
-        elif compiler == 'clang3.6':
+        elif compiler == 'clang4.0':
             return ('ubuntu1604',
                     self._clang_cmake_configure_extra_args(
-                        version_suffix='-3.6'))
-        elif compiler == 'clang3.7':
+                        version_suffix='-4.0'))
+        elif compiler == 'clang5.0':
             return ('ubuntu1604',
                     self._clang_cmake_configure_extra_args(
-                        version_suffix='-3.7'))
+                        version_suffix='-5.0'))
         else:
             raise Exception('Compiler %s not supported.' % compiler)
 
@@ -1425,8 +1425,8 @@ argp.add_argument(
         'gcc7.4',
         'gcc8.3',
         'gcc_musl',
-        'clang3.6',
-        'clang3.7',
+        'clang4.0',
+        'clang5.0',
         'python2.7',
         'python3.5',
         'python3.6',

tools/run_tests/run_tests_matrix.py

@@ -266,8 +266,8 @@ def _create_portability_test_jobs(extra_args=[],
 
     # portability C and C++ on x64
     for compiler in [
-            'gcc4.9', 'gcc5.3', 'gcc7.4', 'gcc8.3', 'gcc_musl', 'clang3.6',
-            'clang3.7'
+            'gcc4.9', 'gcc5.3', 'gcc7.4', 'gcc8.3', 'gcc_musl', 'clang4.0',
+            'clang5.0'
     ]:
         test_jobs += _generate_jobs(languages=['c', 'c++'],
                                     configs=['dbg'],