[Bugfix] Handle gcc unsupported __VA_OPT___ macro (#1881)

Add check to see if `__VA_OPT__` macro is supported, if not, applies `<true_result>` value for `COND()` macro by default.

This has the side-effect/limitation that all protocol names are included in the build, even if the protocol is not available in the code, but _only_ for compilers dat do _not_ support the `__VA_OPT__` macro, notably gcc 4.8.2 (and older).

Resolves #1880

Author: tonhuisman

src/IRmacros.h

@@ -5,6 +5,20 @@
  */
 /// @file IRmacros.h
 
+/**
+ * VA_OPT_SUPPORTED macro to check if __VA_OPT__ is supported
+ * Source: https://stackoverflow.com/a/48045656
+ */
+/// @cond TEST
+#define PP_THIRD_ARG(a, b, c, ...) c
+#define VA_OPT_SUPPORTED_I(...) \
+            PP_THIRD_ARG(__VA_OPT__(, false), true, false, false)
+#define VA_OPT_SUPPORTED VA_OPT_SUPPORTED_I(?)
+/// @endcond
+/**
+ * VA_OPT_SUPPORTED end
+ */
+
 /**
  * COND() Set of macros to facilitate single-line conditional compilation
  * argument checking.
@@ -13,8 +27,14 @@
  * 
  * Usage:
  * COND(<define_to_test>[||/&&<more_define>...], <true_result>, <false_result>)
+ * 
+ * NB: If __VA_OPT__ macro not supported, the <true_result> will be expanded!
  */
 /// @cond TEST
+#if !VA_OPT_SUPPORTED
+// #pragma message("Compiler without __VA_OPT__ support")
+#define COND(cond, a, b) a
+#else  // !VA_OPT_SUPPORTED
 #define NOTHING
 #define EXPAND(...) __VA_ARGS__
 #define STUFF_P(a, ...) __VA_OPT__(a)
@@ -24,6 +44,7 @@
 #define NEGATE(a) VA_TEST(a, a)
 #define COND_P(cond, a, b) STUFF(a, cond)STUFF(b, NEGATE(cond))
 #define COND(cond, a, b) EXPAND(COND_P(cond, a, b))
+#endif  // !VA_OPT_SUPPORTED
 /// @endcond
 /**
  * end of COND() set of macros