[libc] Move b* string functions to strings.h

[abrachet]

Summary

Traditionally these functions are exposed in string*s*.h not string.h

[sivachandra]

Fine with me but lets wait for @gchatelet to tell us if this was intentional.

[gchatelet]

In D141237#4035058, @sivachandra wrote:

Fine with me but lets wait for @gchatelet to tell us if this was intentional.

I didn't set up the td file, it was already there when I added bzero.
+1 on this patch.

libc/include/CMakeLists.txt

add_gen_header(
   GEN_HDR string.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.null_macro
     .llvm-libc-types.size_t
 )
 
 add_gen_header(
+  strings
+  DEF_FILE strings.h.def
+  GEN_HDR strings.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-types.size_t
+)
+
+add_gen_header(
   time
   DEF_FILE time.h.def
   GEN_HDR time.h
   DEPENDS
     .llvm_libc_common_h
     .llvm-libc-macros.time_macros
     .llvm-libc-types.time_t
     .llvm-libc-types.clock_t

libc/include/strings.h.def

+//===-- C standard library header strings.h -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_STRINGS_H
+#define LLVM_LIBC_STRINGS_H
+
+#include <__llvm-libc-common.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_STRINGS_H

libc/spec/llvm_libc_ext.td

 def LLVMLibcExt : StandardSpec<"llvm_libc_ext"> {
-  HeaderSpec String = HeaderSpec<
-      "string.h",
+  HeaderSpec Strings = HeaderSpec<
+      "strings.h",
       [], // Macros
       [], // Types
       [], // Enumerations
       [
           FunctionSpec<
               "bcopy",
               RetValSpec<VoidType>,
               [ArgSpec<ConstVoidPtr>, ArgSpec<VoidPtr>, ArgSpec<SizeTType>]
HeaderSpec Sched = HeaderSpec<
             "__sched_getcpucount",
             RetValSpec<IntType>,
             [ArgSpec<SizeTType>, ArgSpec<ConstCpuSetPtr>]
         >,
       ]
   >;
 
   let Headers = [
-    String,
+    Strings,
     Sched,
     Assert,
   ];
 }