Compile with -Werror=strict-prototypes.

This prevents incorrect invocation of functions.

Almost exclusively updated via dirty search/replaces:

find include -name '*.h' -exec sed -i '' -r 's/\(\);/(void);/g' {} \;
find src -name '*.c' -exec sed -i '' -r 's/\(\)$/(void)/g' {} \;
find src -name '*.c' -exec sed -i '' -r 's/^(((extern|static) )?(void|float|qbool)[^(]+)\(\);/\1(void);/g' {} \;

Followed by a handful of manual cleanups.

Author: dsvensson

CMakeLists.txt

@@ -3,6 +3,8 @@ cmake_minimum_required(VERSION 3.9.0)
 # Set project name and languge.
 project(qwprogs C)
 
+include(CheckCCompilerFlag)
+
 # CMake option for bot support, we check it below and add C preprocessor directive if required.
 option(BOT_SUPPORT "Build with bot support" ON)
 # Option for FTE extensions. We also have some basic support for FTE which does not controlled by this setting.
@@ -152,6 +154,12 @@ if (CMAKE_C_COMPILER_ID STREQUAL "MSVC")
 	target_compile_options(${PROJECT_NAME} PRIVATE /W4)
 else()
 	target_compile_options(${PROJECT_NAME} PRIVATE -Wall)
+
+	check_c_compiler_flag("-Wstrict-prototypes" HAS_CFLAG_STRICT_PROTOTYPES)
+	if (HAS_CFLAG_STRICT_PROTOTYPES)
+		target_compile_options(${PROJECT_NAME} PRIVATE -Werror=strict-prototypes)
+	endif()
+
 	# Do not allow undefined symbols while linking.
 	if(APPLE)
 		target_link_options(${PROJECT_NAME} PRIVATE "-Wl,-undefined,error")