[libc] Migrate to using LIBC_NAMESPACE_DECL for namespace declaration (#98597)

This is a part of #97655.

Author: petrhosek

libc/benchmarks/LibcDefaultImplementations.cpp

@@ -1,8 +1,9 @@
 #include "LibcFunctionPrototypes.h"
+#include "src/__support/macros/config.h"
 #include "llvm/ADT/ArrayRef.h"
 #include <cstddef>
 
-namespace LIBC_NAMESPACE {
+namespace LIBC_NAMESPACE_DECL {
 
 extern void *memcpy(void *__restrict, const void *__restrict, size_t);
 extern void *memmove(void *, const void *, size_t);
@@ -11,7 +12,7 @@ extern void bzero(void *, size_t);
 extern int memcmp(const void *, const void *, size_t);
 extern int bcmp(const void *, const void *, size_t);
 
-} // namespace LIBC_NAMESPACE
+} // namespace LIBC_NAMESPACE_DECL
 
 // List of implementations to test.
 

libc/benchmarks/LibcMemoryBenchmarkMain.cpp

@@ -10,6 +10,7 @@
 #include "LibcBenchmark.h"
 #include "LibcMemoryBenchmark.h"
 #include "MemorySizeDistributions.h"
+#include "src/__support/macros/config.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
@@ -21,7 +22,7 @@
 #include <cstring>
 #include <unistd.h>
 
-namespace LIBC_NAMESPACE {
+namespace LIBC_NAMESPACE_DECL {
 
 extern void *memcpy(void *__restrict, const void *__restrict, size_t);
 extern void *memmove(void *, const void *, size_t);
@@ -30,7 +31,7 @@ extern void bzero(void *, size_t);
 extern int memcmp(const void *, const void *, size_t);
 extern int bcmp(const void *, const void *, size_t);
 
-} // namespace LIBC_NAMESPACE
+} // namespace LIBC_NAMESPACE_DECL
 
 namespace llvm {
 namespace libc_benchmarks {