trace: Workaround GCC bug compiling with old systemtap

cmake/module/FindUSDT.cmake

@@ -36,6 +36,10 @@ if(USDT_INCLUDE_DIR)
   include(CheckCXXSourceCompiles)
   set(CMAKE_REQUIRED_INCLUDES ${USDT_INCLUDE_DIR})
   check_cxx_source_compiles("
+    #if defined(__arm__)
+    #  define STAP_SDT_ARG_CONSTRAINT g
+    #endif
+
     // Setting SDT_USE_VARIADIC lets systemtap (sys/sdt.h) know that we want to use
     // the optional variadic macros to define tracepoints.
     #define SDT_USE_VARIADIC 1