[bazel] Use binary_alias instead of symlinks for ld.lld and friends

Symlinks are poorly supported in Bazel+remote-exec.  Create the links from `ld.lld`,
`ld64.lld`, `lld-link`, `wasm-ld` to `lld` using LLVM's `binary_alias` instead.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D157830

Author: anguslees

utils/bazel/llvm-project-overlay/lld/BUILD.bazel

@@ -4,6 +4,7 @@
 
 load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
 load("//llvm:tblgen.bzl", "gentbl")
+load("//llvm:binary_alias.bzl", "binary_alias")
 load(
     "//:vars.bzl",
     "LLVM_VERSION",
@@ -315,16 +316,15 @@ cc_binary(
 # macOS require that the binary be named "ld64.lld".
 # Windows require that the binary be named "lld-link".
 # WebAssembly builds require that the binary be named "wasm-ld".
-genrule(
-    name = "gen_lld",
-    srcs = [":lld"],
-    outs = [
+[
+    binary_alias(
+        name = name,
+        binary = ":lld",
+    )
+    for name in [
         "ld.lld",
         "ld64.lld",
         "lld-link",
         "wasm-ld",
-    ],
-    cmd =
-        "target=$$(basename $<); for n in ld.lld ld64.lld lld-link wasm-ld; do ln -sf $$target $(@D)/$$n; done",
-    output_to_bindir = 1,
-)
+    ]
+]