Fix a compilation with non-clang/non-gcc compilers

source/common/putilimp.h

Index: source/common/putilimp.h
diff --git a/source/common/putilimp.h b/source/common/putilimp.h
index 430e697b81b5a8a349e80577ec92a3e6c56a03e4..90bae929f41461acf5f40f1a7570e508438adc10 100644
--- a/source/common/putilimp.h
+++ b/source/common/putilimp.h
@@ -236,15 +236,18 @@ typedef size_t uintptr_t;
  */
 #ifdef U_HAVE_CLANG_ATOMICS
     /* Use the predefined value. */
-#elif defined(__clang__) && \
-      __has_builtin(__c11_atomic_load) && \
-      __has_builtin(__c11_atomic_store) && \
-      __has_builtin(__c11_atomic_fetch_add) && \
-      __has_builtin(__c11_atomic_fetch_sub)
+#elif !defined(__clang__)
+#    define U_HAVE_CLANG_ATOMICS 0
+#else
+#if __has_builtin(__c11_atomic_load) && \
+    __has_builtin(__c11_atomic_store) && \
+    __has_builtin(__c11_atomic_fetch_add) && \
+    __has_builtin(__c11_atomic_fetch_sub)
 #    define U_HAVE_CLANG_ATOMICS 1
 #else
 #    define U_HAVE_CLANG_ATOMICS 0
 #endif
+#endif
 
 /*===========================================================================*/
 /** @{ Code alignment                                                        */