Update to AMBuild 2.2.

This is a pretty big diff because SourceMod had lots of multi-arch
workarounds that can now go away. I've also changed 'x64' to 'x86_64' in
many places since this is how AMBuild normalizes it, and it's far too
late to pick the shorter string, so we might as well suck it up.

The --target-archs parameter has been replaced with --targets. It works
the same way.

The default behavior for SDK inclusion is now "present" instead of
"all" since this lowers the burden of storing many SDKs. Official builds
will still be made with --sdks=all.

core/sourcemod.cpp

@@ -182,10 +182,16 @@ bool SourceModBase::InitializeSourceMod(char *error, size_t maxlength, bool late
 	/* There will always be a path by this point, since it was force-set above. */
 	m_GotBasePath = true;
 
+#if defined PLATFORM_X86
+# define SOURCEPAWN_DLL "sourcepawn.jit.x86"
+#else
+# define SOURCEPAWN_DLL "sourcepawn.vm"
+#endif
+
 	/* Attempt to load the JIT! */
 	char file[PLATFORM_MAX_PATH];
 	char myerror[255];
-	g_SMAPI->PathFormat(file, sizeof(file), "%s/bin/" PLATFORM_ARCH_FOLDER "sourcepawn.jit.x86.%s",
+	g_SMAPI->PathFormat(file, sizeof(file), "%s/bin/" PLATFORM_ARCH_FOLDER SOURCEPAWN_DLL ".%s",
 		GetSourceModPath(),
 		PLATFORM_LIB_EXT
 		);
@@ -195,7 +201,7 @@ bool SourceModBase::InitializeSourceMod(char *error, size_t maxlength, bool late
 	{
 		if (error && maxlength)
 		{
-			ke::SafeSprintf(error, maxlength, "%s (failed to load bin/" PLATFORM_ARCH_FOLDER "sourcepawn.jit.x86.%s)", 
+			ke::SafeSprintf(error, maxlength, "%s (failed to load bin/" PLATFORM_ARCH_FOLDER SOURCEPAWN_DLL ".%s)", 
 				myerror,
 				PLATFORM_LIB_EXT);
 		}