SDL: cmake: Force linker to treat input as a C++ program on Haiku.

SDL Commits
1 
From b83a019d68a7d35363830988a2d172d7a348108a Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Wed, 4 Aug 2021 19:22:10 -0400
Subject: [PATCH] cmake: Force linker to treat input as a C++ program on Haiku.

Reference issue #4590.
---
 CMakeLists.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a1bda7bcc..94a6ad10f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,6 +10,10 @@ if(WINDOWS_STORE)
   add_definitions(-DSDL_BUILDING_WINRT=1 -ZW)
 endif()
 
+if (HAIKU)
+  set(LINKER_LANGUAGE CXX)
+endif()
+
 # !!! FIXME: this should probably do "MACOSX_RPATH ON" as a target property
 # !!! FIXME:  for the SDL2 shared library (so you get an
 # !!! FIXME:  install_name ("soname") of "@rpath/libSDL-whatever.dylib"