[cmake] Remove MSVC C4800 override

[RKSimon]

Summary

Remove C4800 : ''type' : forcing value to bool 'true' or 'false' (performance warning)' from the list of forced disabled warnings.

I'm not seeing any regressions in VS2017/VS2019 llvm/clang builds from removing this. I don't have VS2015 at hand to test against.

Hopefully we can remove more of these overrides as some appear to be ancient and targetted against older versions of MSVC.

[rnk]

lgtm

I confirmed that this hasn't been in the default warning set for 2017, which these days I guess is the oldest we support. Feel free to remove other off-by-default warnings, I don't think we need to proactively defend against users adding them to their own cflags, or using old msvc versions.

llvm/trunk/cmake/modules/HandleLLVMOptions.cmake

set(msvc_warning_flags
       -wd4351 # Suppress 'new behavior: elements of array 'array' will be default initialized'
       -wd4456 # Suppress 'declaration of 'var' hides local variable'
       -wd4457 # Suppress 'declaration of 'var' hides function parameter'
       -wd4458 # Suppress 'declaration of 'var' hides class member'
       -wd4459 # Suppress 'declaration of 'var' hides global declaration'
       -wd4503 # Suppress ''identifier' : decorated name length exceeded, name was truncated'
       -wd4624 # Suppress ''derived class' : destructor could not be generated because a base class destructor is inaccessible'
       -wd4722 # Suppress 'function' : destructor never returns, potential memory leak
-      -wd4800 # Suppress ''type' : forcing value to bool 'true' or 'false' (performance warning)'
       -wd4100 # Suppress 'unreferenced formal parameter'
       -wd4127 # Suppress 'conditional expression is constant'
       -wd4512 # Suppress 'assignment operator could not be generated'
       -wd4505 # Suppress 'unreferenced local function has been removed'
       -wd4610 # Suppress '<class> can never be instantiated'
       -wd4510 # Suppress 'default constructor could not be generated'
       -wd4702 # Suppress 'unreachable code'
       -wd4245 # Suppress 'signed/unsigned mismatch'