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

fusl/arch/sh/src/__unmapself.c

+#include "pthread_impl.h"
+
+void __unmapself_sh_mmu(void *, size_t);
+void __unmapself_sh_nommu(void *, size_t);
+
+#if !defined(__SH3__) && !defined(__SH4__)
+#define __unmapself __unmapself_sh_nommu
+#include "dynlink.h"
+#undef CRTJMP
+#define CRTJMP(pc,sp) __asm__ __volatile__( \
+        "mov.l @%0+,r0 ; mov.l @%0,r12 ; jmp @r0 ; mov %1,r15" \
+        : : "r"(pc), "r"(sp) : "r0", "memory" )
+#include "../../../src/thread/__unmapself.c"
+#undef __unmapself
+extern __attribute__((__visibility__("hidden"))) unsigned __sh_nommu;
+#else
+#define __sh_nommu 0
+#endif
+
+void __unmapself(void *base, size_t size)
+{
+        if (__sh_nommu) __unmapself_sh_nommu(base, size);
+        else __unmapself_sh_mmu(base, size);
+}