Fail CI build when not allowed warnings are present

Put -Wno-error after -Wall to make it work properly for clang.

CI/before_script.linux.sh

@@ -14,6 +14,12 @@ if [[ "${BUILD_TESTS_ONLY}" ]]; then
     BUILD_BENCHMARKS=ON
 fi
 
+CXX_FLAGS='-Werror -Wno-error=deprecated-declarations -Wno-error=nonnull -Wno-error=deprecated-copy'
+
+if [[ "${CXX}" == 'clang++' ]]; then
+    CXX_FLAGS="${CXX_FLAGS} -Wno-error=unused-lambda-capture -Wno-error=gnu-zero-variadic-macro-arguments"
+fi
+
 declare -a CMAKE_CONF_OPTS=(
     -DCMAKE_C_COMPILER="${CC:-/usr/bin/cc}"
     -DCMAKE_CXX_COMPILER="${CXX:-/usr/bin/c++}"
@@ -24,6 +30,8 @@ declare -a CMAKE_CONF_OPTS=(
     -DBUILD_SHARED_LIBS=OFF
     -DUSE_SYSTEM_TINYXML=ON
     -DCMAKE_INSTALL_PREFIX=install
+    -DCMAKE_C_FLAGS='-Werror'
+    -DCMAKE_CXX_FLAGS="${CXX_FLAGS}"
 )
 
 if [[ $CI_OPENMW_USE_STATIC_DEPS ]]; then

CMakeLists.txt

@@ -512,7 +512,7 @@ endif()
 
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL GNU OR CMAKE_CXX_COMPILER_ID STREQUAL Clang)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wundef -Wno-unused-parameter -pedantic -Wno-long-long")
+    set(CMAKE_CXX_FLAGS "-Wall -Wextra -Wundef -Wno-unused-parameter -pedantic -Wno-long-long ${CMAKE_CXX_FLAGS}")
     add_definitions( -DBOOST_NO_CXX11_SCOPED_ENUMS=ON )
 
     if (APPLE)