[macOS] Build infrastructure and portability fixes

Build system:
- Enable ObjC++, macOS deployment target, framework linking
- Fix AppleClang detection
- macOS platform name for output directories
- Skip Vulkan on macOS, null graphics without Vulkan dependency
- macOS SDL2 framework detection and discord-rpc macOS sources

Portability fixes:
- mach_absolute_time for macOS tick counting
- _NSGetExecutablePath for macOS
- guard MAP_FIXED_NOREPLACE, ftruncate64->ftruncate
- guard Vulkan include/usage, fix data root for all POSIX

src/xenia/base/clock_posix.cc

@@ -8,6 +8,9 @@
  */
 
 #include <sys/time.h>
+#ifdef __APPLE__
+#include <mach/mach_time.h>
+#endif
 
 #include "xenia/base/assert.h"
 #include "xenia/base/clock.h"
@@ -15,6 +18,12 @@
 namespace xe {
 
 uint64_t Clock::host_tick_frequency_platform() {
+#ifdef __APPLE__
+  mach_timebase_info_data_t info;
+  mach_timebase_info(&info);
+  return (uint64_t)((1000000000ull * (uint64_t)info.denom) /
+                    (uint64_t)info.numer);
+#else
   timespec res;
   int error = clock_getres(CLOCK_MONOTONIC_RAW, &res);
   assert_zero(error);
@@ -22,14 +31,19 @@ uint64_t Clock::host_tick_frequency_platform() {
 
   // Convert nano seconds to hertz. Resolution is 1ns on most systems.
   return 1000000000ull / res.tv_nsec;
+#endif
 }
 
 uint64_t Clock::host_tick_count_platform() {
+#ifdef __APPLE__
+  return mach_absolute_time();
+#else
   timespec tp;
   int error = clock_gettime(CLOCK_MONOTONIC_RAW, &tp);
   assert_zero(error);
 
   return tp.tv_nsec + tp.tv_sec * 1000000000ull;
+#endif
 }
 
 uint64_t Clock::QueryHostSystemTime() {

src/xenia/base/filesystem_posix.cc

@@ -23,6 +23,10 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#if XE_PLATFORM_MAC
+#include <limits.h>
+#include <mach-o/dyld.h>
+#endif
 
 namespace xe {
 
@@ -43,10 +47,26 @@ std::filesystem::path to_path(const std::u16string_view source) {
 namespace filesystem {
 
 std::filesystem::path GetExecutablePath() {
+#if XE_PLATFORM_MAC
+  char path[PATH_MAX];
+  uint32_t size = sizeof(path);
+  if (_NSGetExecutablePath(path, &size) == 0) {
+    char real_path[PATH_MAX];
+    if (realpath(path, real_path)) {
+      return std::string(real_path);
+    }
+    return std::string(path);
+  }
+  return std::string();
+#else
   char buff[FILENAME_MAX] = "";
-  readlink("/proc/self/exe", buff, FILENAME_MAX);
-  std::string s(buff);
-  return s;
+  ssize_t len = readlink("/proc/self/exe", buff, sizeof(buff) - 1);
+  if (len != -1) {
+    buff[len] = '\0';
+    return std::string(buff);
+  }
+  return std::string();
+#endif
 }
 
 std::filesystem::path GetExecutableFolder() {

src/xenia/base/memory_posix.cc

@@ -146,7 +146,9 @@ void* AllocFixed(void* base_address, size_t length,
       }
       return nullptr;
     }
+#ifdef MAP_FIXED_NOREPLACE
     flags |= MAP_FIXED_NOREPLACE;
+#endif
   }
 
   void* result = mmap(base_address, length, prot, flags, -1, 0);
@@ -296,7 +298,7 @@ FileMappingHandle CreateFileMappingHandle(const std::filesystem::path& path,
   if (ret < 0) {
     return kFileMappingHandleInvalid;
   }
-  if (ftruncate64(ret, length) < 0) {
+  if (ftruncate(ret, length) < 0) {
     close(ret);
     shm_unlink(full_path.c_str());
     return kFileMappingHandleInvalid;
@@ -335,7 +337,9 @@ void* MapFileView(FileMappingHandle handle, void* base_address, size_t length,
 
   int flags = MAP_SHARED;
   if (base_address != nullptr) {
+#ifdef MAP_FIXED_NOREPLACE
     flags |= MAP_FIXED_NOREPLACE;
+#endif
   }
 
   void* result = mmap(base_address, length, prot, flags, handle, file_offset);