Make sure we unset the CMAKE_REQUIRED_LIBRARIES variable.

If we don't unset it, all the CMake checks will run with PortAudio
in the library list. This didn't affect those who had PortAudio,
but for select Debian systems without it, it breaks everything.

CMakeLists.txt

@@ -490,6 +490,7 @@ if(NOT ANDROID)
 		int main(int argc, char **argv)
 		{ if(Pa_GetVersion() >= 1890) return 0; else return 1; }"
 		PORTAUDIO)
+	unset(CMAKE_REQUIRED_LIBRARIES)
 	if(PORTAUDIO)
 		message("PortAudio found, enabling mic support")
 		add_definitions(-DHAVE_PORTAUDIO=1)

Externals/enet/CMakeLists.txt

@@ -13,11 +13,10 @@ check_function_exists("gethostbyaddr_r" HAS_GETHOSTBYADDR_R)
 check_function_exists("inet_pton" HAS_INET_PTON)
 check_function_exists("inet_ntop" HAS_INET_NTOP)
 check_struct_has_member("struct msghdr" "msg_flags" "sys/types.h;sys/socket.h" HAS_MSGHDR_FLAGS)
-set(CMAKE_REQUIRED_LIBRARIES "")
 set(CMAKE_EXTRA_INCLUDE_FILES "sys/types.h" "sys/socket.h")
 check_type_size("socklen_t" HAS_SOCKLEN_T BUILTIN_TYPES_ONLY)
 unset(CMAKE_EXTRA_INCLUDE_FILES)
- 
+
 if(HAS_FCNTL)
     add_definitions(-DHAS_FCNTL=1)
 endif()
@@ -42,9 +41,9 @@ endif()
 if(HAS_SOCKLEN_T)
     add_definitions(-DHAS_SOCKLEN_T=1)
 endif()
- 
+
 include_directories(${PROJECT_SOURCE_DIR}/include)
- 
+
 add_library(enet STATIC
         callbacks.c
         compress.c