Make checkedAdd work for long long in MSVC

7 jobs for msvc_overflow in 5 minutes and 2 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #6704492
build

00:04:33

passed #6704497
build_android

00:00:48

passed #6704493
build_clang_libcpp

00:05:01

passed #6704496
build_clazy

00:04:21

passed #6704495
build_mingw64_fedora

00:03:00

passed #6704494
build_ubuntu_16_04

00:02:12

passed #6704491
clang_format

00:01:08