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

fusl/src/setjmp/arm/setjmp.s

+.syntax unified
+.global __setjmp
+.global _setjmp
+.global setjmp
+.type __setjmp,%function
+.type _setjmp,%function
+.type setjmp,%function
+__setjmp:
+_setjmp:
+setjmp:
+        mov ip,r0
+        stmia ip!,{v1,v2,v3,v4,v5,v6,sl,fp,sp,lr}
+        mov r0,#0
+
+        adr r1,1f
+        ldr r2,1f
+        ldr r1,[r1,r2]
+
+        tst r1,#0x260
+        beq 3f
+        tst r1,#0x20
+        beq 2f
+        stc p2, cr4, [ip], #48
+2:      tst r1,#0x40
+        beq 2f
+        .fpu vfp
+        vstmia ip!, {d8-d15}
+        .fpu softvfp
+        .eabi_attribute 10, 0
+        .eabi_attribute 27, 0
+2:      tst r1,#0x200
+        beq 3f
+        stcl p1, cr10, [ip], #8
+        stcl p1, cr11, [ip], #8
+        stcl p1, cr12, [ip], #8
+        stcl p1, cr13, [ip], #8
+        stcl p1, cr14, [ip], #8
+        stcl p1, cr15, [ip], #8
+3:      bx lr
+
+.hidden __hwcap
+1:      .word __hwcap-1b