Clean up build script to just use a toolchain

tools/build.py

 #!/usr/bin/env python3
 
 import argparse
-from contextlib import contextmanager
 import os
 from pathlib import Path
 from typing import Sequence
-import subprocess
 import sys
 import shutil
-import tempfile
 
 from dds_ci import paths
 from self_build import self_build
 BUILD_DIR = ROOT / '_build'
 
 
-@contextmanager
-def _generate_toolchain(cxx: str):
-    with tempfile.NamedTemporaryFile(
-            suffix='-dds-toolchain.dds', mode='wb', delete=False) as f:
-        comp_id = 'GNU'
-        flags = ''
-        link_flags = ''
-        if cxx in ('cl', 'cl.exe'):
-            comp_id = 'MSVC'
-            flags += '/experimental:preprocessor '
-            link_flags += 'rpcrt4.lib '
-        else:
-            flags += '-fconcepts'
-        flags += ' -DSPDLOG_COMPILED_LIB'
-        content = f'''
-            Compiler-ID: {comp_id}
-            C++-Compiler: {cxx}
-            C++-Version: C++17
-            Debug: True
-            Flags: {flags}
-            Link-Flags: {link_flags}
-        '''
-        print('Using generated toolchain file: ' + content)
-        f.write(content.encode('utf-8'))
-        f.close()
-        yield Path(f.name)
-        os.unlink(f.name)
-
-
 def main(argv: Sequence[str]) -> int:
+    # Prior versions of this script took a --cxx argument, but we don't care anymore
     parser = argparse.ArgumentParser()
-    parser.add_argument(
-        '--cxx', help='Path/name of the C++ compiler to use.', required=True)
-    args = parser.parse_args(argv)
+    parser.add_argument('--cxx', help=argparse.SUPPRESS)
+    parser.parse_args(argv)
 
     dds_bootstrap_env_key = 'DDS_BOOTSTRAP_PREV_EXE'
     if dds_bootstrap_env_key not in os.environ:
     print(f'Using previously built DDS executable: {dds_exe}')
     self_deps_get(dds_exe, paths.SELF_TEST_REPO_DIR)
 
-    with _generate_toolchain(args.cxx) as tc_fpath:
-        self_deps_build(dds_exe, tc_fpath, paths.SELF_TEST_REPO_DIR,
-                        ROOT / 'remote.dds')
-        self_build(dds_exe, toolchain=tc_fpath, dds_flags=['--apps'])
+    if os.name == 'nt':
+        tc_fpath = ROOT / 'tools/msvc.dds'
+    else:
+        tc_fpath = ROOT / 'gcc-9.dds'
+
+    self_deps_build(dds_exe, str(tc_fpath), paths.SELF_TEST_REPO_DIR,
+                    ROOT / 'remote.dds')
+    self_build(dds_exe, toolchain=str(tc_fpath), dds_flags=['--apps'])
 
     return 0