backtrace support rework proposal.

Linux/Solaris supports it in the libc however, BSD in general, Haiku
relies on an external library.

CMakeLists.txt

@@ -103,11 +103,21 @@ find_package(OpenGL REQUIRED)
 list(APPEND yquake2IncludeDirectories ${OPENGL_INCLUDE_DIR})
 list(APPEND yquake2OpenGLLinkerFlags ${OPENGL_LIBRARIES})
 
-# FreeBSD needs libexecinfo.
-if(${CMAKE_HOST_SYSTEM_NAME} STREQUAL "FreeBSD")
-	find_library(EXECINFO_LIBRARIES execinfo /usr/lib /usr/local/lib)
-	list(APPEND yquake2ClientLinkerFlags ${EXECINFO_LIBRARIES})
-	list(APPEND yquake2ServerLinkerFlags ${EXECINFO_LIBRARIES})
+# backtrace lookup
+# Some systems like Linux has it within the libc some like the BSD, Haiku ...
+# into an external libexecinfo library
+include(CheckFunctionExists)
+include(CheckLibraryExists)
+check_function_exists(backtrace HAVE_EXECINFO_SYS)
+IF (NOT HAVE_EXECINFO_SYS)
+	check_library_exists(execinfo backtrace "" HAVE_EXECINFO_LIB)
+    if (HAVE_EXECINFO_LIB)
+        list(APPEND yquake2ClientLinkerFlags execinfo)
+        list(APPEND yquake2ServerLinkerFlags execinfo)
+        add_definitions(-DHAVE_EXECINFO)
+    endif()
+else()
+    add_definitions(-DHAVE_EXECINFO)
 endif()
 
 # cURL support.

src/backends/unix/signalhandler.c

@@ -30,7 +30,7 @@
 
 #include "../../common/header/common.h"
 
-#if defined(__GLIBC__) || defined(__FreeBSD__) || defined(__APPLE__)
+#if defined(HAVE_EXECINFO)
 #include <execinfo.h>
 
 void