meson: Check compiler options and Python version

Thanks to William Woodruff for pointing out that -Wcast-align=strict is
a GCC-only option, which causes build errors (instead of just
complaining about an unsupported warning option).

meson.build

@@ -1,18 +1,31 @@
-project('fadec', ['c'], default_options: ['warning_level=3', 'c_std=c99'])
+project('fadec', ['c'], default_options: ['warning_level=3', 'c_std=c99'],
+        meson_version: '>=0.40')
 
 python3 = find_program('python3')
 
+# Check Python version
+py_version_res = run_command(python3, ['--version'])
+py_version = py_version_res.stdout().split(' ')[1]
+if py_version_res.returncode() != 0 or not py_version.version_compare('>=3.6')
+  error('Python 3.6 required, got @0@'.format(py_version))
+endif
+
 if get_option('warning_level').to_int() >= 3
-  add_project_arguments(['-Wmissing-prototypes',
-                         '-Wshadow',
-                         '-Wcast-align=strict',
-                         '-Wwrite-strings',
-                         '-Winline',
-                         '-Wswitch-default',
-                         '-Wstrict-prototypes',
-                         '-Wundef',
-                         '-Wno-overlength-strings'],
-                        language: 'c')
+  extra_warnings = [
+    '-Wmissing-prototypes', '-Wshadow',  '-Wwrite-strings', '-Wswitch-default',
+    '-Winline', '-Wstrict-prototypes', '-Wundef',
+    # We have strings longer than 4095 characters
+    '-Wno-overlength-strings',
+    # GCC 8 requires an extra option for strict cast alignment checks, Clang
+    # always warns, even on architectures without alignment requirements.
+    '-Wcast-align', '-Wcast-align=strict',
+  ]
+  cc = meson.get_compiler('c')
+  foreach warning : extra_warnings
+    if cc.has_argument(warning)
+      add_project_arguments(warning, language: 'c')
+    endif
+  endforeach
 endif
 
 generate_args = []

parseinstrs.py

@@ -601,9 +601,9 @@ def encode_table(entries):
         for idx, alt, (enc, immsz, tys_i, opc_s) in zip(indices, alt_list, dedup):
             descs += f"[{idx}] = {{ .enc = ENC_{enc}, .immsz = {immsz}, .tys = {tys_i:#x}, .opc = {opc_s}, .alt = {alt} }},\n"
 
-    mnemonics_lut = {mnem: i for i, mnem in enumerate(sorted(mnemonics.keys()))}
-    mnemonics_tab = "\n".join("FE_MNEMONIC(%s,%d)"%entry for entry in mnemonics_lut.items())
-    return mnemonics_tab, descs
+    mnem_list = sorted(mnemonics.keys())
+    mnem_tab = "".join(f"FE_MNEMONIC({m},{i})\n" for i, m in enumerate(mnem_list))
+    return mnem_tab, descs
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
@@ -624,8 +624,8 @@ if __name__ == "__main__":
 
     mnemonics = sorted({desc.mnemonic for _, desc in entries})
 
-    decode_mnems_lines = ["FD_MNEMONIC(%s,%d)"%e[::-1] for e in enumerate(mnemonics)]
-    args.decode_mnems.write("\n".join(decode_mnems_lines))
+    decode_mnems_lines = [f"FD_MNEMONIC({m},{i})\n" for i, m in enumerate(mnemonics)]
+    args.decode_mnems.write("".join(decode_mnems_lines))
 
     modes = [32, 64]
     table = Table(root_count=len(args.modes))