Bump version of gcc and clang (#29594)

templates/tools/dockerfile/test/cxx_clang_6_x64/Dockerfile.template

@@ -14,7 +14,7 @@
   # See the License for the specific language governing permissions and
   # limitations under the License.
   
-  FROM silkeh/clang:4
+  FROM silkeh/clang:6
   
   RUN apt-get update && apt-get install -y build-essential curl git time wget zip && apt-get clean
   <%include file="../../run_tests_python_deps.include"/>

templates/tools/dockerfile/test/cxx_gcc_6_x64/Dockerfile.template

@@ -14,7 +14,7 @@
   # See the License for the specific language governing permissions and
   # limitations under the License.
   
-  FROM gcc:5
+  FROM gcc:6
   
   RUN apt-get update && apt-get install -y curl git time wget zip && apt-get clean
   <%include file="../../run_tests_python_deps.include"/>

tools/dockerfile/test/cxx_clang_6_x64/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM silkeh/clang:4
+FROM silkeh/clang:6
 
 RUN apt-get update && apt-get install -y build-essential curl git time wget zip && apt-get clean
 #====================

tools/dockerfile/test/cxx_gcc_6_x64/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM gcc:5
+FROM gcc:6
 
 RUN apt-get update && apt-get install -y curl git time wget zip && apt-get clean
 #====================

tools/run_tests/run_tests.py

@@ -484,8 +484,8 @@ class CLanguage(object):
 
         if compiler == 'default' or compiler == 'cmake':
             return ('debian11', [])
-        elif compiler == 'gcc5':
-            return ('gcc_5', [])
+        elif compiler == 'gcc6':
+            return ('gcc_6', [])
         elif compiler == 'gcc10.2':
             return ('debian11', [])
         elif compiler == 'gcc10.2_openssl102':
@@ -496,8 +496,8 @@ class CLanguage(object):
             return ('gcc_11', [])
         elif compiler == 'gcc_musl':
             return ('alpine', [])
-        elif compiler == 'clang4':
-            return ('clang_4', self._clang_cmake_configure_extra_args())
+        elif compiler == 'clang6':
+            return ('clang_6', self._clang_cmake_configure_extra_args())
         elif compiler == 'clang13':
             return ('clang_13', self._clang_cmake_configure_extra_args())
         else:
@@ -1551,12 +1551,12 @@ argp.add_argument(
     '--compiler',
     choices=[
         'default',
-        'gcc5',
+        'gcc6',
         'gcc10.2',
         'gcc10.2_openssl102',
         'gcc11',
         'gcc_musl',
-        'clang4',
+        'clang6',
         'clang13',
         'python2.7',
         'python3.5',

tools/run_tests/run_tests_matrix.py

@@ -300,7 +300,7 @@ def _create_portability_test_jobs(extra_args=[],
 
     # portability C and C++ on x64
     for compiler in [
-            'gcc5', 'gcc10.2_openssl102', 'gcc11', 'gcc_musl', 'clang4',
+            'gcc6', 'gcc10.2_openssl102', 'gcc11', 'gcc_musl', 'clang6',
             'clang13'
     ]:
         test_jobs += _generate_jobs(languages=['c', 'c++'],