[clang][Driver] Default to /usr/bin/ld on Solaris

`clang` currently requires the native linker on Solaris:

  - It passes `-C` to `ld` which GNU `ld` doesn't understand.

  - To use `gld`, one needs to pass the correct `-m EMU` option to select
    the right emulation.  Solaris `ld` cannot handle that option.

So far I've worked around this by passing `-DCLANG_DEFAULT_LINKER=/usr/bin/ld`
to `cmake`.  However, if someone forgets this, it depends on the user's
`PATH` whether or not `clang` finds the correct linker, which doesn't make
for a good user experience.

While it would be nice to detect the linker flavor at runtime, this is more
involved.  Instead, this patch defaults to `/usr/bin/ld` on Solaris.  This
doesn't work on its own, however: a link fails with

  clang-12: error: unable to execute command: Executable "x86_64-pc-solaris2.11-/usr/bin/ld" doesn't exist!

I avoid this by leaving absolute paths alone in `ToolChain::GetLinkerPath`.

Tested on `amd64-pc-solaris2.11`, `sparcv9-sun-solaris2.11`, and
`x86_64-pc-linux-gnu`.

Differential Revision: https://reviews.llvm.org/D84029

1 files changed, 7 insertions, 2 deletions

diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 2984537..7be83ca 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -568,8 +568,13 @@ std::string ToolChain::GetLinkerPath() const {
   }
   // If we're passed -fuse-ld= with no argument, or with the argument ld,
   // then use whatever the default system linker is.
-  if (UseLinker.empty() || UseLinker == "ld")
-    return GetProgramPath(getDefaultLinker());
+  if (UseLinker.empty() || UseLinker == "ld") {
+    const char *DefaultLinker = getDefaultLinker();
+    if (llvm::sys::path::is_absolute(DefaultLinker))
+      return std::string(DefaultLinker);
+    else
+      return GetProgramPath(DefaultLinker);
+  }
 
   // Extending -fuse-ld= to an absolute or relative path is unexpected. Checking
   // for the linker flavor is brittle. In addition, prepending "ld." or "ld64."