[libc] fix clang-tidy llvm-header-guard warnings (llvm#82679)

Towards the goal of getting `ninja libc-lint` back to green, fix the numerous
instances of:

    warning: header guard does not follow preferred style [llvm-header-guard]

This is because many of our header guards start with `__LLVM` rather than
`LLVM`.

To filter just these warnings:

    $ ninja -k2000 libc-lint 2>&1 | grep llvm-header-guard

To automatically apply fixits:

    $ find libc/src libc/include libc/test -name \*.h | \
        xargs -n1 -I {} clang-tidy {} -p build/compile_commands.json \
        -checks='-*,llvm-header-guard' --fix --quiet

Some manual cleanup is still necessary as headers that were missing header
guards outright will have them inserted before the license block (we prefer
them after).

Author: nickdesaulniers

libc/include/__llvm-libc-common.h

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC___COMMON_H
-#define LLVM_LIBC___COMMON_H
+#ifndef LLVM_LIBC_COMMON_H
+#define LLVM_LIBC_COMMON_H
 
 #ifdef __cplusplus
 
@@ -51,4 +51,4 @@
 
 #endif // __cplusplus
 
-#endif // LLVM_LIBC___COMMON_H
+#endif // LLVM_LIBC_COMMON_H

libc/include/llvm-libc-macros/containerof-macro.h

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H
-#define __LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H
+#ifndef LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H
+#define LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H
 
 #include <llvm-libc-macros/offsetof-macro.h>
 
@@ -17,4 +17,4 @@
     (type *)(void *)((const char *)__ptr - offsetof(type, member));            \
   })
 
-#endif // __LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H
+#endif // LLVM_LIBC_MACROS_CONTAINEROF_MACRO_H

libc/include/llvm-libc-macros/fcntl-macros.h

@@ -1,8 +1,8 @@
-#ifndef __LLVM_LIBC_MACROS_FCNTL_MACROS_H
-#define __LLVM_LIBC_MACROS_FCNTL_MACROS_H
+#ifndef LLVM_LIBC_MACROS_FCNTL_MACROS_H
+#define LLVM_LIBC_MACROS_FCNTL_MACROS_H
 
 #ifdef __linux__
 #include "linux/fcntl-macros.h"
 #endif
 
-#endif // __LLVM_LIBC_MACROS_FCNTL_MACROS_H
+#endif // LLVM_LIBC_MACROS_FCNTL_MACROS_H

libc/include/llvm-libc-macros/features-macros.h

@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_FEATURES_MACROS_H
-#define __LLVM_LIBC_MACROS_FEATURES_MACROS_H
+#ifndef LLVM_LIBC_MACROS_FEATURES_MACROS_H
+#define LLVM_LIBC_MACROS_FEATURES_MACROS_H
 
 #define __LLVM_LIBC__ 1
 
-#endif // __LLVM_LIBC_MACROS_FEATURES_MACROS_H
+#endif // LLVM_LIBC_MACROS_FEATURES_MACROS_H

libc/include/llvm-libc-macros/fenv-macros.h

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_FENV_MACROS_H
-#define __LLVM_LIBC_MACROS_FENV_MACROS_H
+#ifndef LLVM_LIBC_MACROS_FENV_MACROS_H
+#define LLVM_LIBC_MACROS_FENV_MACROS_H
 
 #define FE_DIVBYZERO 1
 #define FE_INEXACT 2
@@ -24,4 +24,4 @@
 
 #define FE_DFL_ENV ((fenv_t *)-1)
 
-#endif // __LLVM_LIBC_MACROS_FENV_MACROS_H
+#endif // LLVM_LIBC_MACROS_FENV_MACROS_H

libc/include/llvm-libc-macros/file-seek-macros.h

@@ -6,11 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H
-#define __LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H
+#ifndef LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H
+#define LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H
 
 #define SEEK_SET 0
 #define SEEK_CUR 1
 #define SEEK_END 2
 
-#endif // __LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H
+#endif // LLVM_LIBC_MACROS_FILE_SEEK_MACROS_H

libc/include/llvm-libc-macros/float-macros.h

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_FLOAT_MACROS_H
-#define __LLVM_LIBC_MACROS_FLOAT_MACROS_H
+#ifndef LLVM_LIBC_MACROS_FLOAT_MACROS_H
+#define LLVM_LIBC_MACROS_FLOAT_MACROS_H
 
 // Suppress `#include_next is a language extension` warnings.
 #ifdef __clang__
@@ -169,4 +169,4 @@
 
 // TODO: Add FLT16 and FLT128 constants.
 
-#endif // __LLVM_LIBC_MACROS_FLOAT_MACROS_H
+#endif // LLVM_LIBC_MACROS_FLOAT_MACROS_H

libc/include/llvm-libc-macros/generic-error-number-macros.h

@@ -6,8 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H
-#define __LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H
+#ifndef LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H
+#define LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H
 
 #define EPERM 1
 #define ENOENT 2
@@ -45,4 +45,4 @@
 #define ERANGE 34
 #define EILSEQ 35
 
-#endif // __LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H
+#endif // LLVM_LIBC_MACROS_GENERIC_ERROR_NUMBER_MACROS_H

libc/include/llvm-libc-macros/gpu/time-macros.h

@@ -6,9 +6,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef __LLVM_LIBC_MACROS_GPU_TIME_MACROS_H
-#define __LLVM_LIBC_MACROS_GPU_TIME_MACROS_H
+#ifndef LLVM_LIBC_MACROS_GPU_TIME_MACROS_H
+#define LLVM_LIBC_MACROS_GPU_TIME_MACROS_H
 
 #define CLOCKS_PER_SEC 1000000
 
-#endif // __LLVM_LIBC_MACROS_GPU_TIME_MACROS_H
+#endif // LLVM_LIBC_MACROS_GPU_TIME_MACROS_H

libc/include/llvm-libc-macros/inttypes-macros.h

@@ -5,8 +5,8 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
-#ifndef __LLVM_LIBC_MACROS_INTTYPES_MACROS_H
-#define __LLVM_LIBC_MACROS_INTTYPES_MACROS_H
+#ifndef LLVM_LIBC_MACROS_INTTYPES_MACROS_H
+#define LLVM_LIBC_MACROS_INTTYPES_MACROS_H
 
 // fprintf/scanf format macros.
 // POSIX.1-2008, Technical Corrigendum 1, XBD/TC1-2008/0050 [211] is applied.
@@ -286,4 +286,4 @@
 #define SCNxMAX __UINTMAX_FMTx__
 #define SCNxPTR __UINTPTR_FMTx__
 
-#endif // __LLVM_LIBC_MACROS_INTTYPES_MACROS_H
+#endif // LLVM_LIBC_MACROS_INTTYPES_MACROS_H