[bazel] Add layering-check

In the same vein as https://reviews.llvm.org/D141553
Enable the feature globally to ensure layering and catch circular dependencies
(https://llvm.org/docs/CodingStandards.html#library-layering).

Differential Revision: https://reviews.llvm.org/D143678

Author: gchatelet

Diff for: utils/bazel/.bazelrc

@@ -22,6 +22,9 @@ build --dynamic_mode=off
 # based on compilation_mode.
 build --strip=never
 
+# Add layering check to all projects.
+build --features=layering_check
+
 ###############################################################################
 # Options to select different strategies for linking potential dependent
 # libraries. The default leaves it disabled.

Diff for: utils/bazel/llvm-project-overlay/libc/utils/MPFRWrapper/BUILD.bazel

@@ -27,6 +27,13 @@ cc_library(
     name = "mpfr_wrapper",
     srcs = ["MPFRUtils.cpp"],
     hdrs = ["MPFRUtils.h"],
+    # Disable layering check when using mpfr_system.
+    features = select(
+        {
+            "//conditions:default": [],
+            "//libc:mpfr_system": ["-layering_check"],
+        },
+    ),
     deps = [
         "//libc:__support_common",
         "//libc:__support_cpp_bit",
@@ -36,9 +43,9 @@ cc_library(
         "//libc:__support_fputil_fp_bits",
         "//libc:__support_fputil_platform_defs",
         "//libc:libc_root",
-        "//libc/utils/MPFRWrapper:mpfr_impl",
         "//libc/test/UnitTest:LibcUnitTest",
         "//libc/test/UnitTest:fp_test_helpers",
+        "//libc/utils/MPFRWrapper:mpfr_impl",
         "//libc/utils/testutils:libc_test_utils",
     ],
 )