ARROW-2505: [C++] Disable MSVC warning C4800

Author: Antoine Pitrou <[email protected]>

Closes #1980 from pitrou/ARROW-2505-disable-msvc-warning-c4800 and squashes the following commits:

f586da2 <Antoine Pitrou> Fix command-line option
bb064db <Antoine Pitrou> ARROW-2505:  Disable MSVC warning C4800

Author: pitrou

cpp/cmake_modules/SetupCxxFlags.cmake

@@ -167,6 +167,11 @@ else()
   endif()
 endif()
 
+# Disable annoying "performance warning" about int-to-bool conversion
+if ("${COMPILER_FAMILY}" STREQUAL "msvc")
+  set(CXX_COMMON_FLAGS "${CXX_COMMON_FLAGS} /wd4800")
+endif()
+
 # if build warning flags is set, add to CXX_COMMON_FLAGS
 if (BUILD_WARNING_FLAGS)
   # Use BUILD_WARNING_FLAGS with BUILD_WARNING_LEVEL=everything to disable