[libunwind] Remove unnecessary strcpy dependency (#72043)

libunwind uses a minimal set of necessary standard library functions,
basically just `memset` and `memcpy`. There is a single use of `strcpy`
to copy the bytes `"CLNGUNW"` into a `uint64_t` object. This is both an
arguably odd use of the `strcpy` function as well as it unnecessarily
widens the set of library functions that must be available to build
libunwind, which can be an obstacle in baremetal scenarios. This change
simply replaces this one `strcpy` with the more fundamental `memcpy`.

Author: michael-kenzel

libunwind/src/UnwindLevel1-gcc-ext.c

@@ -143,7 +143,7 @@ _Unwind_Backtrace(_Unwind_Trace_Fn callback, void *ref) {
   // Create a mock exception object for force unwinding.
   _Unwind_Exception ex;
   memset(&ex, '\0', sizeof(ex));
-  strcpy((char *)&ex.exception_class, "CLNGUNW");
+  memcpy(&ex.exception_class, "CLNGUNW", sizeof(ex.exception_class));
 #endif
 
   // walk each frame

libunwind/test/forceunwind.pass.cpp

@@ -61,7 +61,7 @@ __attribute__((noinline)) void foo() {
 #if defined(_LIBUNWIND_ARM_EHABI)
   // Create a mock exception object.
   memset(e, '\0', sizeof(*e));
-  strcpy(reinterpret_cast<char *>(&e->exception_class), "CLNGUNW");
+  memcpy(&e->exception_class, "CLNGUNW", sizeof(e->exception_class));
 #endif
   _Unwind_ForcedUnwind(e, stop, (void *)&foo);
 }