[bazel] Move MC header usage from Support to tblgen

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.

Differential Revision: https://reviews.llvm.org/D111835

Author: rnk

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

@@ -187,7 +187,6 @@ cc_library(
     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",
@@ -453,6 +452,11 @@ cc_library(
         "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