[lldb] [lit] Fix finding lld-link when it is not in 'compiler dir'

[mgorny]

Summary

Fix the build helper to find lld-link via PATH lookup, rather than
making a fragile assumption that it will be present in the 'compiler
directory'. This fixes tests on Gentoo where clang and lld
are installed in different directories.

[labath]

lldb/lit/helper/build.py

291–295

How about we replace all of this with a call like linker_path = find_executable(name, [compiler_dir] + search_paths) ?

294–296

find_executable returns None on failure, so this needs to be adjusted.

[mgorny]

Updated to use find_executable() unconditionally.

[labath]

lgtm

lldb/lit/helper/build.py

296

linker_path isn't going to be terribly useful here when it's none. Probably just replace it with name.

[mgorny]

lldb/lit/helper/build.py

296

Indeed, thanks for catching this.

lldb/lit/helper/build.py

def __init__(self, toolchain_type, args):
             selected_target_version = os.path.basename(compiler_parent_dir)
             if selected_target_version != self.msvc_arch_str:
                 host_dir = os.path.dirname(compiler_parent_dir)
                 self.compiler = os.path.join(host_dir, self.msvc_arch_str, 'cl.exe')
                 if self.verbose:
                     print('Using alternate compiler "{0}" to match selected target.'.format(self.compiler))
 
         if self.mode == 'link' or self.mode == 'compile-and-link':
-            self.linker = self._find_linker('link') if toolchain_type == 'msvc' else self._find_linker('lld-link')
+            self.linker = self._find_linker('link') if toolchain_type == 'msvc' else self._find_linker('lld-link', args.tools_dir)
             if not self.linker:
                 raise ValueError('Unable to find an appropriate linker.')
 
         self.compile_env, self.link_env = self._get_visual_studio_environment()
 
-    def _find_linker(self, name):
-        if sys.platform == 'win32':
-            name = name + '.exe'
+    def _find_linker(self, name, search_paths=[]):
         compiler_dir = os.path.dirname(self.compiler)
-        linker_path = os.path.join(compiler_dir, name)
-        if not os.path.exists(linker_path):
+        linker_path = find_executable(name, [compiler_dir] + search_paths)
+        if linker_path is None:
             raise ValueError('Could not find \'{}\''.format(linker_path))
         return linker_path
 
     def _get_vc_install_dir(self):
         dir = os.getenv('VCINSTALLDIR', None)
         if dir:
             if self.verbose:
                 print('Using %VCINSTALLDIR% {}'.format(dir))
             return dir