[libc] Enable wide-read memory operations by default on Linux

Summary:
This patch changes the linux build to use the wide reads on the memory
operations by default. These memory functions will now potentially read
outside of the bounds explicitly allowed by the current function. While
technically undefined behavior in the standard, plenty of C library
implementations do this. it will not cause a segmentation fault on linux
as long as you do not cross a page boundary, and because we are only
*reading* memory it should not have atomic effects.

Author: jhuber6

libc/config/linux/config.json

@@ -0,0 +1,7 @@
+{
+  "string": {
+    "LIBC_CONF_STRING_UNSAFE_WIDE_READ": {
+      "value": true
+    }
+  }
+}

libc/src/string/memory_utils/aarch64/inline_strlen.h

@@ -17,14 +17,15 @@
 namespace LIBC_NAMESPACE_DECL {
 
 namespace neon {
-[[maybe_unused]] LIBC_INLINE size_t string_length(const char *src) {
+[[maybe_unused]] LIBC_INLINE static size_t string_length(const char *src) {
   using Vector __attribute__((may_alias)) = uint8x8_t;
 
   uintptr_t misalign_bytes = reinterpret_cast<uintptr_t>(src) % sizeof(Vector);
-  Vector *block_ptr = reinterpret_cast<Vector *>(src - misalign_bytes);
+  const Vector *block_ptr =
+      reinterpret_cast<const Vector *>(src - misalign_bytes);
   Vector v = *block_ptr;
   Vector vcmp = vceqz_u8(v);
-  uint64x1_t cmp_mask = vreinterpret_u64_s8(vcmp);
+  uint64x1_t cmp_mask = vreinterpret_u64_u8(vcmp);
   uint64_t cmp = vget_lane_u64(cmp_mask, 0);
   cmp = cmp >> (misalign_bytes << 3);
   if (cmp)
@@ -34,7 +35,7 @@ namespace neon {
     ++block_ptr;
     v = *block_ptr;
     vcmp = vceqz_u8(v);
-    cmp_mask = vreinterpret_u64_s8(vcmp);
+    cmp_mask = vreinterpret_u64_u8(vcmp);
     cmp = vget_lane_u64(cmp_mask, 0);
     if (cmp)
       return static_cast<size_t>(reinterpret_cast<uintptr_t>(block_ptr) -