common: rename --clang to --gem5-clang

The option was hard to understand, and this would cause ambiguity
if we ever support something else with the same option, e.g. rootfs
or userland executables.

README.adoc

@@ -12399,8 +12399,8 @@ TODO test properly, benchmark vs GCC.
 
 ....
 sudo apt-get install clang
-./build-gem5 --clang
+./build-gem5 --gem5-clang
-./run --clang --emulator gem5
+./run --emulator gem5 --gem5-clang
 ....
 
 ==== gem5 sanitation build

build-gem5

@@ -117,7 +117,7 @@ https://github.com/cirosantilli/linux-kernel-module-cheat-regression#gem5-unit-t
             targets = [self.env['gem5_unit_test_target']]
         else:
             targets = [self.env['gem5_executable']]
-        if self.env['clang']:
+        if self.env['gem5_clang']:
             extra_env = {
                 'CC': 'clang',
                 'CXX': 'clang++',

common.py

@@ -216,14 +216,6 @@ CPU architecture to use. If given multiple times, run the action
 for each arch sequentially in that order. If one of them fails, stop running.
 Valid archs: {}
 '''.format(arches_string)
-        )
-        self.add_argument(
-            '--clang',
-            default=False,
-            help='''\
-Build with clang as much as possible. Set the build-id to clang by default unless
-one is given explicitly. Currently supported components: gem5.
-'''
         )
         self.add_argument(
             '--dry-run',
@@ -343,6 +335,13 @@ Default: {}
             default=consts['build_type_default'],
             help='gem5 build type, most often used for "debug" builds.'
         )
+        self.add_argument(
+            '--gem5-clang',
+            default=False,
+            help='''\
+Build gem5 with clang and set the --gem5-build-id to 'clang' by default.
+'''
+        )
         self.add_argument(
             '--gem5-source-dir',
             help='''\
@@ -678,7 +677,7 @@ Incompatible archs are skipped.
         if not env['_args_given']['gem5_build_id']:
             if env['_args_given']['gem5_worktree']:
                 env['gem5_build_id'] = env['gem5_worktree']
-            elif env['_args_given']['clang']:
+            elif env['_args_given']['gem5-clang']:
                 env['gem5_build_id'] = 'clang'
             else:
                 env['gem5_build_id'] = consts['default_build_id']