[lldb][Mach-O] Initialize cputype/cpusubtype in test corefiles

TestFirmwareCorefiles.py has a helper utility, create-empty-corefile.cpp,
which creates corefiles with different metadata to specify the
binary that should be loaded.  It normally uses an actual binary's
UUID for the metadata, and it uses the binary's cputype/cpusubtype
for the corefile's mach header.

There is one test where it creates a corefile with metadata for a
UUID that cannot be found -- it is given no binary -- and in that
case, the cputype/cpusubtype it sets in the core file mach header
was uninitialized data.  Through luck, on Darwin systems, the
uninitialized data typically matched a CPU_TYPE from machine.h and
the test would work.  But when the value doens't match one of thoes
defines, lldb would reject the corefile entirely, and the test would
fail.  This has been an infrequent failure on the CI bots for a
while and I couldn't ever repo it.  There's a recent configuration
where it was happening every time and I was able to track it down.

rdar://141727563

Author: jasonmolenda

lldb/test/API/macosx/lc-note/firmware-corefile/create-empty-corefile.cpp

@@ -189,6 +189,14 @@ void add_lc_segment(std::vector<std::vector<uint8_t>> &loadcmds,
 
 std::string get_uuid_from_binary(const char *fn, cpu_type_t &cputype,
                                  cpu_subtype_t &cpusubtype) {
+// We may be given a file, set reasonable values.
+#if defined(__x86_64__)
+  cputype = CPU_TYPE_X86;
+  cpusubtype = CPU_SUBTYPE_X86_ALL;
+#else
+  cputype = CPU_TYPE_ARM64;
+  cpusubtype = CPU_SUBTYPE_ARM64_ALL;
+#endif
   if (strlen(fn) == 0)
     return {};