[libc][bazel] Convert "errno" to libc_support_library. (#130368)

This shouldn't really be a "libc_function" since it can be used as a
dependency of various other support libraries and functions, and doesn't
correspond to a well-defined endpoint that the users may want to
explicitly depend on (if they depend on it implicitly through a
libc_function whose implementation relies on errno, the dependency will
be pulled in normally). Remove special handling for "errno" in the Bazel
test rules.

This is one more cleanup step unlocking the plan outlined in #130327

Author: vonosmas

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

@@ -1598,9 +1598,9 @@ libc_support_library(
     ],
 )
 
-############################### errno targets ################################
+############################### errno ########################################
 
-libc_function(
+libc_support_library(
     name = "errno",
     srcs = ["src/errno/libc_errno.cpp"],
     hdrs = ["src/errno/libc_errno.h"],

utils/bazel/llvm-project-overlay/libc/test/libc_test_rules.bzl

@@ -27,14 +27,14 @@ def libc_test(name, srcs, libc_function_deps = [], copts = [], deps = [], local_
       local_defines: The list of target local_defines if any.
       **kwargs: Attributes relevant for a libc_test. For example, name, srcs.
     """
-    all_function_deps = libc_function_deps + ["//libc:errno"]
     native.cc_test(
         name = name,
         srcs = srcs,
         local_defines = local_defines + LIBC_CONFIGURE_OPTIONS,
-        deps = [libc_internal_target(d) for d in all_function_deps] + [
+        deps = [libc_internal_target(d) for d in libc_function_deps] + [
             "//libc/test/UnitTest:LibcUnitTest",
             "//libc:__support_macros_config",
+            "//libc:errno",
             "//libc:func_aligned_alloc",
             "//libc:func_free",
             "//libc:func_malloc",

utils/bazel/llvm-project-overlay/libc/test/src/stdlib/BUILD.bazel

@@ -186,7 +186,7 @@ libc_test_library(
         "//libc:__support_cpp_type_traits",
         "//libc:__support_ctype_utils",
         "//libc:__support_macros_properties_architectures",
-        "//libc:errno.__internal__",
+        "//libc:errno",
         "//libc/test/UnitTest:LibcUnitTest",
     ],
 )