[libc] Default to byte_per_byte instead of erroring (#131340)

Summary:
Right now a lot of the memory functions error if we don't have specific
handling for them. This is weird because we have a generic
implementation that should just be used whenever someone hasn't written
a more optimized version. This allows us to use the `libc` headers with
more architectures from the `shared/` directory without worrying about
it breaking.

Author: jhuber6

libc/src/string/memory_utils/inline_bcmp.h

@@ -25,11 +25,9 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/inline_bcmp.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_BCMP inline_bcmp_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
+#else
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_BCMP inline_bcmp_byte_per_byte
-#else
-#error "Unsupported architecture"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/string/memory_utils/inline_memcmp.h

@@ -24,11 +24,9 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/inline_memcmp.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCMP inline_memcmp_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
+#else
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCMP inline_memcmp_byte_per_byte
-#else
-#error "Unsupported architecture"
 #endif
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/string/memory_utils/inline_memcpy.h

@@ -28,14 +28,12 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/inline_memcpy.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_ARM)
-#include "src/string/memory_utils/generic/byte_per_byte.h"
-#define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_byte_per_byte
 #elif defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/builtin.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_builtin
 #else
-#error "Unsupported architecture"
+#include "src/string/memory_utils/generic/byte_per_byte.h"
+#define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_byte_per_byte
 #endif
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/string/memory_utils/inline_memmove.h

@@ -11,7 +11,7 @@
 
 #include "src/__support/macros/attributes.h" // LIBC_INLINE
 #include "src/__support/macros/config.h"     // LIBC_NAMESPACE_DECL
-#include <stddef.h> // size_t, ptrdiff_t
+#include <stddef.h>                          // size_t, ptrdiff_t
 
 #if defined(LIBC_TARGET_ARCH_IS_X86)
 #include "src/string/memory_utils/x86_64/inline_memmove.h"
@@ -29,10 +29,6 @@
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_SMALL_SIZE                        \
   inline_memmove_no_small_size
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_FOLLOW_UP inline_memmove_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_ARM)
-#include "src/string/memory_utils/generic/byte_per_byte.h"
-#define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_SMALL_SIZE                        \
-  inline_memmove_no_small_size
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_FOLLOW_UP                         \
   inline_memmove_byte_per_byte
 #elif defined(LIBC_TARGET_ARCH_IS_GPU)
@@ -41,7 +37,9 @@
   inline_memmove_no_small_size
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_FOLLOW_UP inline_memmove_builtin
 #else
-#error "Unsupported architecture"
+#include "src/string/memory_utils/generic/byte_per_byte.h"
+#define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE_SMALL_SIZE                        \
+  inline_memmove_no_small_size
 #endif
 
 namespace LIBC_NAMESPACE_DECL {

libc/src/string/memory_utils/inline_memset.h

@@ -24,14 +24,12 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/inline_memset.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_riscv
-#elif defined(LIBC_TARGET_ARCH_IS_ARM)
-#include "src/string/memory_utils/generic/byte_per_byte.h"
-#define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_byte_per_byte
 #elif defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/builtin.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_builtin
 #else
-#error "Unsupported architecture"
+#include "src/string/memory_utils/generic/byte_per_byte.h"
+#define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_byte_per_byte
 #endif
 
 namespace LIBC_NAMESPACE_DECL {