Add LIBSAMPLERATE_ENABLE_WARNINGS to generically enable warnings

Useful for (and used in) CI
Some defines required to fix MSVC warnings

.travis.yml

@@ -29,6 +29,6 @@ env:
 script:
   - mkdir build
   - cd build
-  - cmake -DBUILD_SHARED_LIBS=$CMAKE_SHARED -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_C_FLAGS="-Wall -Wextra -Werror" ..
+  - cmake -DBUILD_SHARED_LIBS=$CMAKE_SHARED -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DLIBSAMPLERATE_ENABLE_WARNINGS=ON ..
   - cat config.h
   - cmake --build . --config $BUILD_TYPE && ctest --output-on-failure -C $BUILD_TYPE

CMakeLists.txt

@@ -10,6 +10,7 @@ endif()
 option(LIBSAMPLERATE_TESTS "Enable to generate test targets" ${IS_ROOT_PROJECT})
 option(LIBSAMPLERATE_EXAMPLES "Enable to generate examples" ${IS_ROOT_PROJECT})
 option(LIBSAMPLERATE_INSTALL "Enable to add install directives" ${IS_ROOT_PROJECT})
+option(LIBSAMPLERATE_ENABLE_WARNINGS "Enable compiler warnings and fail compile if any triggers" OFF)
 
 list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake)
 
@@ -106,6 +107,15 @@ target_include_directories(samplerate PUBLIC
 	${PROJECT_SOURCE_DIR}/src
   ${CMAKE_CURRENT_BINARY_DIR})
 
+if(LIBSAMPLERATE_ENABLE_WARNINGS)
+    if(MSVC)
+        target_compile_options(samplerate PUBLIC /W3 /WX)
+        target_compile_options(samplerate PUBLIC /wd4305 /wd4244) # Disable truncation warning double->float
+    else()
+        target_compile_options(samplerate PUBLIC -Wall -Wextra -pedantic -Werror)
+    endif()
+endif()
+
 if(NEED_MATH)
     target_link_libraries(samplerate PUBLIC m)
 endif()
@@ -126,6 +136,9 @@ if(LIBSAMPLERATE_TESTS)
 		if(FFTW_FOUND)
 			target_link_libraries(${testName} PUBLIC ${FFTW_LIBRARY})
 		endif()
+        if(MSVC)
+            target_compile_definitions(${testName} PUBLIC _CRT_SECURE_NO_WARNINGS _CRT_OBSOLETE_NO_WARNINGS)
+        endif()
 		add_test(NAME ${testName} COMMAND ${testName})
 	endforeach(testSrc)
 endif()