(#1118) Treat warning as errors only on CI

Because during development it's super annoying

.travis.yml

@@ -13,5 +13,5 @@ compiler:
 script:
   - mkdir build/
   - cd build/
-  - cmake ..
+  - cmake -DNOTHING_CI=ON ..
   - make -k

CMakeLists.txt

@@ -1,6 +1,8 @@
 cmake_minimum_required(VERSION 3.13)
 project(nothing)
 
+set(NOTHING_CI OFF CACHE BOOL "Indicates whether the build is running on CI or not")
+
 if(WIN32)
   if(MINGW)
     add_compile_definitions(SDL_MAIN_HANDLED) # https://stackoverflow.com/a/25089610
@@ -170,7 +172,6 @@ if(("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU") OR ("${CMAKE_C_COMPILER_ID}" STREQU
   set(CMAKE_C_FLAGS
     "${CMAKE_C_FLAGS} \
      -Wall \
-     -Werror \
      -Wextra \
      -Wconversion \
      -Wunused \
@@ -198,12 +199,14 @@ if(("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU") OR ("${CMAKE_C_COMPILER_ID}" STREQU
      -std=c11 \
      -ggdb \
      -O3")
+  if (${NOTHING_CI})
+     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Werror")
+  endif()
   target_link_libraries(nothing m)
 elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
   set(CMAKE_C_FLAGS
     "${CMAKE_C_FLAGS} \
     /Wall \
-    /WX \
     /wd4127 \
     /wd4201 \
     /wd4204 \
@@ -217,6 +220,9 @@ elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
     /wd5045 \
     /wd4200 \
     /D \"_CRT_SECURE_NO_WARNINGS\"")
+  if (${NOTHING_CI})
+     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} /WX")
+  endif()
 endif()
 if(MINGW)
   target_link_libraries(nothing hid setupapi Imm32 Version winmm)

appveyor.yml

@@ -32,9 +32,9 @@ build_script:
   - cd build
   - ps: |
        if ($isWindows -and $env:BUILD_TYPE -eq 'mingw') {
-           C:\msys64\usr\bin\bash.exe -lc "cmake .. -G 'MSYS Makefiles'"
+           C:\msys64\usr\bin\bash.exe -lc "cmake .. -G 'MSYS Makefiles' -DNOTHING_CI=ON"
            C:\msys64\usr\bin\bash.exe -lc "cmake --build ."
        } else {
-           cmake ..
+           cmake .. -DNOTHING_CI=ON
            cmake --build .
        }