Removing PYBIND11_NOINLINE_FORCED and enhancing comments for PYBIND11_NOINLINE.

Author: rwgk

include/pybind11/detail/common.h

@@ -96,34 +96,21 @@
 #  endif
 #endif
 
-// For CUDA, GCC7, GCC8 (and maybe some other platforms):
-// PYBIND11_NOINLINE_FORCED is incompatible with `-Wattributes -Werror`.
-// When defining PYBIND11_NOINLINE_FORCED, it is best to also use
-// `-Wno-attributes` (or not to use `-Werror` and ignore the warnings).
-#if !defined(PYBIND11_NOINLINE_FORCED) && \
-    (defined(__CUDACC__) || \
-     (defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8)))
-#  define PYBIND11_NOINLINE_DISABLED
-#endif
-
-// Note: Forward declarations should never be `inline`:
+// The PYBIND11_NOINLINE macro is for function DEFINITIONS.
+// In contrast, FORWARD DECLARATIONS should never use this macro:
 // https://stackoverflow.com/questions/9317473/forward-declaration-of-inline-functions
-#if defined(PYBIND11_NOINLINE_DISABLED)
+#if defined(PYBIND11_NOINLINE_DISABLED) // Option for maximum portability and experimentation.
 #  define PYBIND11_NOINLINE inline
 #elif defined(_MSC_VER)
 #  define PYBIND11_NOINLINE __declspec(noinline) inline
 #else
 #  define PYBIND11_NOINLINE __attribute__ ((noinline)) inline
 #endif
 
-// DECISION TO BE MADE before this PR is merged:
-// ----------------------------------------------------------------------------
-// This code and the 9 x 2 pragma blocks referring to
-// PYBIND11_NOINLINE_GCC_PRAGMA_ATTRIBUTES_NEEDED could be purged.
-// ----------------------------------------------------------------------------
 #if !defined(PYBIND11_NOINLINE_DISABLED)
 #    if (defined(__CUDACC__) || (defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8)))          \
         && !defined(PYBIND11_NOINLINE_GCC_PRAGMA_ATTRIBUTES_NEEDED)
+// Only CUDA version known/tested (as of August 2021): CUDA 11, Ubuntu 20.04
 #        define PYBIND11_NOINLINE_GCC_PRAGMA_ATTRIBUTES_NEEDED
 #    elif defined(__INTEL_COMPILER)
 // The following pragma cannot be pop'ed: