[compiler-rt][libunwind] Support aarch64 without FPU (#111235)

These two libraries don't build for `-march=armv8-a+nofp
-mabi=aapcs-soft` as a couple of uses of floating point instructions and
registers have crept in.

In libunwind, skip save/restore of FPU registers on targets without them.
In compiler-rt, fall back to the old C implementation of __arm_sc_memset when
the target doesn't have an FPU.

---------

Signed-off-by: Keith Packard <keithp@keithp.com>

libunwind/src/UnwindRegistersRestore.S

@@ -658,7 +658,7 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto)
   ldp    x26,x27, [x0, #0x0D0]
   ldp    x28,x29, [x0, #0x0E0]
   ldr    x30,     [x0, #0x100]  // restore pc into lr
-
+#if defined(__ARM_FP) && __ARM_FP != 0
   ldp    d0, d1,  [x0, #0x110]
   ldp    d2, d3,  [x0, #0x120]
   ldp    d4, d5,  [x0, #0x130]
@@ -676,7 +676,7 @@ DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto)
   ldp    d28,d29, [x0, #0x1F0]
   ldr    d30,     [x0, #0x200]
   ldr    d31,     [x0, #0x208]
-
+#endif
   // Finally, restore sp. This must be done after the last read from the
   // context struct, because it is allocated on the stack, and an exception
   // could clobber the de-allocated portion of the stack after sp has been

libunwind/src/UnwindRegistersSave.S

@@ -746,6 +746,7 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
   str    x1,      [x0, #0x0F8]
   str    x30,     [x0, #0x100]    // store return address as pc
   // skip cpsr
+#if defined(__ARM_FP) && __ARM_FP != 0
   stp    d0, d1,  [x0, #0x110]
   stp    d2, d3,  [x0, #0x120]
   stp    d4, d5,  [x0, #0x130]
@@ -763,6 +764,7 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
   stp    d28,d29, [x0, #0x1F0]
   str    d30,     [x0, #0x200]
   str    d31,     [x0, #0x208]
+#endif
   mov    x0, #0                   // return UNW_ESUCCESS
   ret