feat: add string manipulation functions derived from musl libc

This commit introduces a variety of string manipulation functions, including:
- `memmem`: Searches for a substring in a memory area.
- `memmove`: Safely copies memory areas, handling overlaps.
- `mempcpy`: Copies memory and returns a pointer to the end of the destination.
- `memrchr`: Finds the last occurrence of a character in a memory area.
- `memset`: Fills a memory area with a specified value.
- `rindex`: Returns the last occurrence of a character in a string.
- `stpcpy` and `stpncpy`: Copies strings and returns a pointer to the end.
- `strcat`, `strchr`, `strcspn`, `strlcat`, `strlcpy`, `strlen`, `strncat`, `strncmp`, `strncpy`, `strnlen`, `strpbrk`, `strrchr`, `strstr`, `strtok`, and `strtok_r`: Various string manipulation functions for concatenation, searching, and tokenization.

Assembly implementations for `memcpy`, `memmove`, and `memset` are also included for optimized performance on x86_64 architectures.

1 files changed, 17 insertions, 0 deletions

diff --git a/na/include/libc-shim/limits.h b/na/include/libc-shim/limits.h
new file mode 100644
index 0000000..a1d546e
--- /dev/null
+++ b/na/include/libc-shim/limits.h
@@ -0,0 +1,17 @@
+/* Shim: limits for musl string functions (memmem uses SIZE_MAX) */
+#ifndef _LIMITS_H
+#define _LIMITS_H
+
+#define CHAR_BIT   8
+#define UCHAR_MAX  255
+#define SCHAR_MAX  127
+#define SCHAR_MIN  (-128)
+#define INT_MAX    2147483647
+#define INT_MIN    (-INT_MAX - 1)
+#define UINT_MAX   4294967295U
+#define LONG_MAX   9223372036854775807L
+#define LONG_MIN   (-LONG_MAX - 1L)
+#define ULONG_MAX  18446744073709551615UL
+#define SIZE_MAX   ULONG_MAX
+
+#endif