Declare a fallback architecture not yet considered by upstream project.

diff --git a/src/tbb/tools_api/ittnotify_config.h b/src/tbb/tools_api/ittnotify_config.h
index 001d42e0..2e68f738 100644
--- a/src/tbb/tools_api/ittnotify_config.h
+++ b/src/tbb/tools_api/ittnotify_config.h
@@ -180,6 +180,11 @@
 #  define ITT_ARCH_ARM64  6
 #endif /* ITT_ARCH_ARM64 */
 
+/* Fallback for other architectures */
+#ifndef ITT_ARCH_GENERIC
+#  define ITT_ARCH_GENERIC 99
+#endif /* ITT_ARCH_GENERIC */
+
 #ifndef ITT_ARCH_LOONGARCH64
 #  define ITT_ARCH_LOONGARCH64  7
 #endif /* ITT_ARCH_LOONGARCH64 */
@@ -209,6 +214,8 @@
 #    define ITT_ARCH ITT_ARCH_ARM64
 #  elif defined __powerpc64__
 #    define ITT_ARCH ITT_ARCH_PPC64
+#  elif
+#    define ITT_ARCH ITT_ARCH_GENERIC
 #  elif defined __loongarch__
 #    define ITT_ARCH ITT_ARCH_LOONGARCH64
 #  elif defined __s390__ || defined __s390x__