Clang configuration: apply defaults rather than using configure_gcc

This isn't as precise, but will avoid the cost of process invocation.
Such cost is considerable on Windows and appears to be around 100ms on
macOS.

Author: tautschnig

src/cbmc/cbmc_parse_options.cpp

@@ -548,12 +548,6 @@ int cbmc_parse_optionst::doit()
     gcc_version.get("gcc");
     configure_gcc(gcc_version);
   }
-  else if(config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-  {
-    gcc_versiont gcc_version;
-    gcc_version.get("clang");
-    configure_gcc(gcc_version);
-  }
 
   if(cmdline.isset("test-preprocessor"))
     return test_c_preprocessor(ui_message_handler)

src/cprover/cprover_parse_options.cpp

@@ -131,13 +131,6 @@ int cprover_parse_optionst::main()
       gcc_version.get("gcc");
       configure_gcc(gcc_version);
     }
-    else if(
-      config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-    {
-      gcc_versiont gcc_version;
-      gcc_version.get("clang");
-      configure_gcc(gcc_version);
-    }
 
     console_message_handlert message_handler;
     null_message_handlert null_message_handler;

src/goto-analyzer/goto_analyzer_parse_options.cpp

@@ -421,12 +421,6 @@ int goto_analyzer_parse_optionst::doit()
     gcc_version.get("gcc");
     configure_gcc(gcc_version);
   }
-  else if(config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-  {
-    gcc_versiont gcc_version;
-    gcc_version.get("clang");
-    configure_gcc(gcc_version);
-  }
 
   goto_model = initialize_goto_model(cmdline.args, ui_message_handler, options);
 

src/goto-diff/goto_diff_parse_options.cpp

@@ -107,12 +107,6 @@ int goto_diff_parse_optionst::doit()
     gcc_version.get("gcc");
     configure_gcc(gcc_version);
   }
-  else if(config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-  {
-    gcc_versiont gcc_version;
-    gcc_version.get("clang");
-    configure_gcc(gcc_version);
-  }
 
   if(process_goto_program(options, goto_model1))
     return CPROVER_EXIT_INTERNAL_ERROR;

src/goto-instrument/goto_instrument_parse_options.cpp

@@ -139,13 +139,6 @@ int goto_instrument_parse_optionst::doit()
       gcc_version.get("gcc");
       configure_gcc(gcc_version);
     }
-    else if(
-      config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-    {
-      gcc_versiont gcc_version;
-      gcc_version.get("clang");
-      configure_gcc(gcc_version);
-    }
 
     {
       const bool validate_only = cmdline.isset("validate-goto-binary");

src/goto-synthesizer/goto_synthesizer_parse_options.cpp

@@ -73,12 +73,6 @@ int goto_synthesizer_parse_optionst::doit()
     gcc_version.get("gcc");
     configure_gcc(gcc_version);
   }
-  else if(config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-  {
-    gcc_versiont gcc_version;
-    gcc_version.get("clang");
-    configure_gcc(gcc_version);
-  }
 
   update_max_malloc_size(goto_model, ui_message_handler);
 

src/libcprover-cpp/api.cpp

@@ -69,12 +69,6 @@ api_sessiont::api_sessiont(const api_optionst &options)
     gcc_version.get("gcc");
     configure_gcc(gcc_version);
   }
-  else if(config.ansi_c.preprocessor == configt::ansi_ct::preprocessort::CLANG)
-  {
-    gcc_versiont gcc_version;
-    gcc_version.get("clang");
-    configure_gcc(gcc_version);
-  }
 }
 
 api_sessiont::~api_sessiont() = default;

src/util/config.cpp

@@ -986,6 +986,13 @@ bool configt::set(const cmdlinet &cmdline)
     ansi_c.os=configt::ansi_ct::ost::OS_MACOS;
     ansi_c.mode = ansi_ct::flavourt::CLANG;
     ansi_c.preprocessor=ansi_ct::preprocessort::CLANG;
+    // configure_gcc sets these with additional version-of-clang level of
+    // detail, but the below are reasonable defaults for modern clang
+    // installations
+    ansi_c.__float128_is_keyword = true;
+    ansi_c.float16_type = true;
+    ansi_c.bf16_type = true;
+    ansi_c.fp16_type = true;
   }
   else if(os == "linux" || os == "solaris" || os == "netbsd" || os == "hurd")
   {
@@ -1000,6 +1007,13 @@ bool configt::set(const cmdlinet &cmdline)
     ansi_c.os=configt::ansi_ct::ost::OS_LINUX;
     ansi_c.mode=ansi_ct::flavourt::CLANG;
     ansi_c.preprocessor=ansi_ct::preprocessort::CLANG;
+    // configure_gcc sets these with additional version-of-clang level of
+    // detail, but the below are reasonable defaults for modern clang
+    // installations
+    ansi_c.__float128_is_keyword = true;
+    ansi_c.float16_type = true;
+    ansi_c.bf16_type = true;
+    ansi_c.fp16_type = true;
   }
   else
   {