Port to 2.1 - Fix performance regression in Guid.NewGuid on OSX (#29457)

We have recently removed dependency on the libuuid for Guid creation. Unfortunately,
while the perf on Linux has improved, we have not noticed that the perf on OSX
degraded 10 fold.

This change fixes it by modifying the implementation of the underlying
SystemNative_GetNonCryptographicallySecureRandomBytes to use arc4random
like the uuid_generate_random that we were using before the libuuid dependency
removal does.

src/Native/Unix/Common/pal_config.h.in

@@ -28,6 +28,7 @@
 #cmakedefine01 HAVE_TIOCGWINSZ
 #cmakedefine01 HAVE_SCHED_GETAFFINITY
 #cmakedefine01 HAVE_SCHED_SETAFFINITY
+#cmakedefine01 HAVE_ARC4RANDOM
 #cmakedefine01 KEVENT_HAS_VOID_UDATA
 #cmakedefine01 HAVE_FDS_BITS
 #cmakedefine01 HAVE_PRIVATE_FDS_BITS

src/Native/Unix/System.Native/pal_random.cpp

@@ -11,6 +11,7 @@
 #include <time.h>
 #include <errno.h>
 
+#include "pal_config.h"
 /*
 
 Generate random bytes. The generated bytes are not cryptographically strong.
@@ -20,6 +21,9 @@ extern "C" void SystemNative_GetNonCryptographicallySecureRandomBytes(uint8_t* b
 {
     assert(buffer != NULL);
 
+#if HAVE_ARC4RANDOM
+    arc4random_buf(buffer, (size_t)bufferLength);
+#else
     static volatile int rand_des = -1;
     long num = 0;
     static bool sMissingDevURandom;
@@ -93,4 +97,5 @@ extern "C" void SystemNative_GetNonCryptographicallySecureRandomBytes(uint8_t* b
         *(buffer + i) ^= num;
         num >>= 8;
     }
+#endif // HAS_ARC4RANDOM
 }

src/Native/Unix/configure.cmake

@@ -140,6 +140,10 @@ check_function_exists(
     sched_setaffinity
     HAVE_SCHED_SETAFFINITY)
 
+check_function_exists(
+    arc4random
+    HAVE_ARC4RANDOM)
+
 check_symbol_exists(
     TIOCGWINSZ
     "sys/ioctl.h"