Allow use of "$(location //foo)" in compiler_options

[carpenterjc]

We use "$(location //foo)" syntax https://bazel.build/reference/be/make-variables#predefined_label_variables and have patched 19.2 to call expand_location.

Can we request support for make variable substitution using technique.

Example patch for 19.2:

diff --git dotnet/private/rules/csharp/binary.bzl dotnet/private/rules/csharp/binary.bzl
index 005e5e1..ebfd504 100644
--- dotnet/private/rules/csharp/binary.bzl
+++ dotnet/private/rules/csharp/binary.bzl
@@ -15,6 +15,12 @@ load("//dotnet/private/transitions:tfm_transition.bzl", "tfm_transition")

 def _compile_action(ctx, tfm):
     toolchain = ctx.toolchains["//dotnet:toolchain_type"]
+
+    compiler_options = []
+    for opt in ctx.attr.compiler_options:
+        added = ctx.expand_location(opt, ctx.attr.compile_data)
+        compiler_options.append(added)
+
     return AssemblyAction(
         ctx.actions,
         ctx.executable._compiler_wrapper_bat if ctx.target_platform_has_constraint(ctx.attr._windows_constraint[platform_common.ConstraintValueInfo]) else ctx.executable._compiler_wrapper_sh,
@@ -53,7 +59,7 @@ def _compile_action(ctx, tfm):
         is_analyzer = False,
         is_language_specific_analyzer = False,
         analyzer_configs = ctx.files.analyzer_configs,
-        compiler_options = ctx.attr.compiler_options,
+        compiler_options = compiler_options,
         is_windows = ctx.target_platform_has_constraint(ctx.attr._windows_constraint[platform_common.ConstraintValueInfo]),
     )

[purkhusid]

This sounds like a very reasonable request. If you have the capacity to create a PR then I would happily accept it.