We are having a problem with linker lookup on Windows.
When the driver tries to locate a program by its name, e.g. a linker, it scans the paths provided by the toolchain using ScanDirForExecutable and then, if fails, uses llvm::sys::findProgramByName, which on Windows searches the CWD and system path. ScanDirForExecutable disregards file extensions, so search in the toolchain-provided dirs on Windows fails. llvm::sys::findProgramByName is aware of extensions via the "PATHEXT" env variable (it also has ".exe" hardcoded). However, our linker is not in the CWD or system path, thus search fails.
ScanDirForExecutable should respect file extenstions like findProgramByName does. One way of doing so is to make the system dependent llvm::sys::path::access function aware of extensions similarly to findProgramByName. Or the whole ScanDirForExecutable can be made system dependent and add an extension on Windows before passing the path to llvm::sys::fs::can_execute.
Does such a patch look reasonable? Any opinions / ideas will be much appreciated.