Add a "fork" of musl as //fusl.

fusl/src/mman/mmap.c

Index: fusl/src/mman/mmap.c
diff --git a/fusl/src/mman/mmap.c b/fusl/src/mman/mmap.c
new file mode 100644
index 0000000000000000000000000000000000000000..b85f25ca083e8aeff9a20f645a2e4d0f4bd701b6
--- /dev/null
+++ b/fusl/src/mman/mmap.c
@@ -0,0 +1,37 @@
+#include <unistd.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <stdint.h>
+#include <limits.h>
+#include "syscall.h"
+#include "libc.h"
+
+static void dummy(void) { }
+weak_alias(dummy, __vm_wait);
+
+#define UNIT SYSCALL_MMAP2_UNIT
+#define OFF_MASK ((-0x2000ULL << (8*sizeof(long)-1)) | (UNIT-1))
+
+void *__mmap(void *start, size_t len, int prot, int flags, int fd, off_t off)
+{
+	if (off & OFF_MASK) {
+		errno = EINVAL;
+		return MAP_FAILED;
+	}
+	if (len >= PTRDIFF_MAX) {
+		errno = ENOMEM;
+		return MAP_FAILED;
+	}
+	if (flags & MAP_FIXED) {
+		__vm_wait();
+	}
+#ifdef SYS_mmap2
+	return (void *)syscall(SYS_mmap2, start, len, prot, flags, fd, off/UNIT);
+#else
+	return (void *)syscall(SYS_mmap, start, len, prot, flags, fd, off);
+#endif
+}
+
+weak_alias(__mmap, mmap);
+
+LFS64(mmap);