UserspaceEmulator+LibX86: Turn on -O3 optimization for emulation code

Since this code is performance-sensitive, let's have the compiler do
whatever it can to help us with the most important files.

This yields a ~8% speedup.

DevTools/UserspaceEmulator/Emulator.cpp

@@ -38,6 +38,10 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#if defined(__GNUC__) && !defined(__clang__)
+#    pragma GCC optimize("O3")
+#endif
+
 //#define DEBUG_SPAM
 
 namespace UserspaceEmulator {
@@ -171,6 +175,7 @@ void Emulator::dump_backtrace()
         if (!ret_ptr)
             return;
         symbol = m_elf->symbolicate(ret_ptr, &offset);
+        if (!symbol.is_null())
             printf("> %#08x  %s +%#x\n", ret_ptr, symbol.characters(), offset);
 
         frame_ptr = m_mmu.read32({ 0x20, frame_ptr });

DevTools/UserspaceEmulator/SoftCPU.cpp

@@ -30,6 +30,10 @@
 #include <stdio.h>
 #include <string.h>
 
+#if defined(__GNUC__) && !defined(__clang__)
+#    pragma GCC optimize("O3")
+#endif
+
 //#define MEMORY_DEBUG
 
 namespace UserspaceEmulator {

Libraries/LibX86/Instruction.cpp

@@ -29,6 +29,10 @@
 #include <LibX86/Interpreter.h>
 #include <stdio.h>
 
+#if defined(__GNUC__) && !defined(__clang__)
+#    pragma GCC optimize("O3")
+#endif
+
 namespace X86 {
 
 enum IsLockPrefixAllowed {