[bazel] Move MC header usage from Support to tblgen

[rnk]

Summary

After the TargetRegistry.h move, nothing in Support includes headers
from MC. However, files in tablegen use MC headers, so we must add an
entry for them in tblgen srcs.

[GMNGeoffrey]

A step in the right direction, thanks!

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

455

Can you note that this is a layering violation and we can't depend on MC because it creates circular dependencies?

[rnk]

• elaborate

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

]) + select({
         "//conditions:default": glob([
             "lib/Support/Unix/*.h",
             "lib/Support/Unix/*.inc",
         ]),
     }),
     hdrs = glob([
         "include/llvm/Support/**/*.h",
         "include/llvm/ADT/*.h",
-        "include/llvm/MC/*.h",  # TODO(maskray): Fix the layering issue.
     ]) + [
         "include/llvm-c/Core.h",
         "include/llvm-c/DataTypes.h",
         "include/llvm-c/DisassemblerTypes.h",
         "include/llvm-c/Error.h",
         "include/llvm-c/ErrorHandling.h",
         "include/llvm-c/ExternC.h",
         "include/llvm-c/Support.h",

 )
 
 cc_library(
     name = "tblgen",
     srcs = glob([
         "utils/TableGen/*.cpp",
         "utils/TableGen/GlobalISel/*.cpp",
 
+        # Some tablegen sources include headers from MC, so these have to be
+        # listed here. MC uses headers produced by tablegen, so it cannot be a
+        # regular dependency.
+        "include/llvm/MC/*.h",
+
         # We have to include these headers here as well as in the `hdrs` below
         # to allow the `.cpp` files to use file-relative-inclusion to find
         # them, even though consumers of this library use inclusion relative to
         # `utils/TableGen` with the `strip_includes_prefix` of this library.
         # This mixture appears to be incompatible with header modules.
         "utils/TableGen/*.h",
         "utils/TableGen/GlobalISel/*.h",
     ]),