Revert "build: build with -O0 if Clang >= 16 is used"

This reverts commit fb05fddd7d. After
1554b5cb61 ("Update seastar submodule"),
which fixed a coroutine bug in Seastar, it is no longer necessary.

Also revert the related "build: drop the warning on -O0 might fail tests"
(894039d444).

cmake/mode.common.cmake

@@ -40,19 +40,3 @@ check_cxx_compiler_flag(${_stack_usage_threshold_flag} _stack_usage_flag_support
 if(_stack_usage_flag_supported)
   string(APPEND CMAKE_CXX_FLAGS " ${_stack_usage_threshold_flag}")
 endif()
-
-if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 16)
-  # workaround https://github.com/llvm/llvm-project/issues/62842
-  set(_original_level "${Seastar_OptimizationLevel_${build_mode}}")
-  set(_safe_level "0")
-  if(NOT _original_level STREQUAL _safe_level)
-    message(WARNING
-      "Changing optimization level from -O${_original_level} to -O${_safe_level} "
-      "due to https://github.com/llvm/llvm-project/issues/62842.")
-    string(REPLACE " -O${_original_level} " " -O${_safe_level} "
-      CMAKE_CXX_FLAGS_${build_mode}
-      "${CMAKE_CXX_FLAGS_${build_mode}}")
-  endif()
-  unset(_original_level)
-  unset(_safe_level)
-endif()

configure.py

@@ -18,7 +18,6 @@ import sys
 import tempfile
 import textwrap
 from distutils.spawn import find_executable
-from pkg_resources import parse_version
 
 curdir = os.getcwd()
 
@@ -164,40 +163,6 @@ def flag_supported(flag, compiler):
     return try_compile(flags=['-Werror'] + split, compiler=compiler)
 
 
-class OptimizationLevel:
-    warned = False
-
-    @classmethod
-    def _warn(cls, safe_level) -> None:
-        if cls.warned:
-            # only prints this warning for a single time
-            return
-        print('\033[91mWARN\033[00m: '
-              f'Changing optimization level to "-O{safe_level}" '
-              'due to https://github.com/llvm/llvm-project/issues/62842.')
-        cls.warned = True
-
-    def __call__(self, cxx_compiler, default_level):
-        # workaround https://github.com/llvm/llvm-project/issues/62842
-        if 'clang' not in cxx_compiler:
-            return default_level
-
-        proc = subprocess.run([cxx_compiler, '--version'],
-                              capture_output=True,
-                              check=True,
-                              text=True)
-        matched = re.match(r'clang version (\d+\.\d+.\d+)', proc.stdout)
-        if matched is None:
-            raise Exception(f'Unable to tell version of {cxx_compiler}')
-        if parse_version(matched.group(1)) < parse_version('16.0.0'):
-            return default_level
-        safe_level = '0'
-        if default_level == safe_level:
-            return default_level
-        self._warn(safe_level)
-        return safe_level
-optimization_level = OptimizationLevel()
-
 def linker_flags(compiler):
     src_main = 'int main(int argc, char **argv) { return 0; }'
     link_flags = ['-fuse-ld=lld']
@@ -1466,8 +1431,7 @@ for mode_level in args.mode_o_levels:
     modes[mode]['optimization-level'] = level
 
 for mode in modes:
-    level = optimization_level(args.cxx, modes[mode]["optimization-level"])
-    modes[mode]['cxxflags'] += f' -O{level}'
+    modes[mode]['cxxflags'] += f' -O{modes[mode]["optimization-level"]}'
 
 optimization_flags = [
     '--param inline-unit-growth=300', # gcc