fix: allow the ABI string to be forced (#2602)

include/pybind11/detail/internals.h

@@ -160,43 +160,54 @@ struct type_info {
 #endif
 
 /// Let's assume that different compilers are ABI-incompatible.
-#if defined(_MSC_VER)
+/// A user can manually set this string if they know their
+/// compiler is compatible.
+#ifndef PYBIND11_COMPILER_TYPE
+#  if defined(_MSC_VER)
 #    define PYBIND11_COMPILER_TYPE "_msvc"
-#elif defined(__INTEL_COMPILER)
+#  elif defined(__INTEL_COMPILER)
 #    define PYBIND11_COMPILER_TYPE "_icc"
-#elif defined(__clang__)
+#  elif defined(__clang__)
 #    define PYBIND11_COMPILER_TYPE "_clang"
-#elif defined(__PGI)
+#  elif defined(__PGI)
 #    define PYBIND11_COMPILER_TYPE "_pgi"
-#elif defined(__MINGW32__)
+#  elif defined(__MINGW32__)
 #    define PYBIND11_COMPILER_TYPE "_mingw"
-#elif defined(__CYGWIN__)
+#  elif defined(__CYGWIN__)
 #    define PYBIND11_COMPILER_TYPE "_gcc_cygwin"
-#elif defined(__GNUC__)
+#  elif defined(__GNUC__)
 #    define PYBIND11_COMPILER_TYPE "_gcc"
-#else
+#  else
 #    define PYBIND11_COMPILER_TYPE "_unknown"
+#  endif
 #endif
 
-#if defined(_LIBCPP_VERSION)
+/// Also standard libs
+#ifndef PYBIND11_STDLIB
+#  if defined(_LIBCPP_VERSION)
 #    define PYBIND11_STDLIB "_libcpp"
-#elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
+#  elif defined(__GLIBCXX__) || defined(__GLIBCPP__)
 #    define PYBIND11_STDLIB "_libstdcpp"
-#else
+#  else
 #    define PYBIND11_STDLIB ""
+#  endif
 #endif
 
 /// On Linux/OSX, changes in __GXX_ABI_VERSION__ indicate ABI incompatibility.
-#if defined(__GXX_ABI_VERSION)
+#ifndef PYBIND11_BUILD_ABI
+#  if defined(__GXX_ABI_VERSION)
 #    define PYBIND11_BUILD_ABI "_cxxabi" PYBIND11_TOSTRING(__GXX_ABI_VERSION)
-#else
+#  else
 #    define PYBIND11_BUILD_ABI ""
+#  endif
 #endif
 
-#if defined(WITH_THREAD)
+#ifndef PYBIND11_INTERNALS_KIND
+#  if defined(WITH_THREAD)
 #    define PYBIND11_INTERNALS_KIND ""
-#else
+#  else
 #    define PYBIND11_INTERNALS_KIND "_without_thread"
+#  endif
 #endif
 
 #define PYBIND11_INTERNALS_ID "__pybind11_internals_v" \