[Driver] Override default location of config files

If directory for config files was specified in project configuration
using parameters CLANG_CONFIG_FILE_SYSTEM_DIR or CLANG_CONFIG_FILE_USER_DIR,
it was not overriden by command-line option `--config-system-dir=` or
`--config-user-dir=` that specified empty path.

This change corrects the behavior. It fixes the issue
llvm#56836 ([clang] [test]
test/Driver/config-file-errs.c fails if CLANG_CONFIG_FILE_SYSTEM_DIR is
specified).

Author: spavloff

clang/lib/Driver/Driver.cpp

@@ -970,23 +970,19 @@ bool Driver::loadConfigFile() {
       SmallString<128> CfgDir;
       CfgDir.append(
           CLOptions->getLastArgValue(options::OPT_config_system_dir_EQ));
-      if (!CfgDir.empty()) {
-        if (llvm::sys::fs::make_absolute(CfgDir).value() != 0)
-          SystemConfigDir.clear();
-        else
-          SystemConfigDir = static_cast<std::string>(CfgDir);
-      }
+      if (CfgDir.empty() || llvm::sys::fs::make_absolute(CfgDir))
+        SystemConfigDir.clear();
+      else
+        SystemConfigDir = static_cast<std::string>(CfgDir);
     }
     if (CLOptions->hasArg(options::OPT_config_user_dir_EQ)) {
       SmallString<128> CfgDir;
       CfgDir.append(
           CLOptions->getLastArgValue(options::OPT_config_user_dir_EQ));
-      if (!CfgDir.empty()) {
-        if (llvm::sys::fs::make_absolute(CfgDir).value() != 0)
-          UserConfigDir.clear();
-        else
-          UserConfigDir = static_cast<std::string>(CfgDir);
-      }
+      if (CfgDir.empty() || llvm::sys::fs::make_absolute(CfgDir))
+        UserConfigDir.clear();
+      else
+        UserConfigDir = static_cast<std::string>(CfgDir);
     }
   }