MSVC warning don't recognized as error

[redboltz]

I noticed that windows build has many warnings.

For example https://github.com/msgpack/msgpack-c/runs/362778135#step:4:505

I wrote CMakeLists.txt that warnings are regard as errors.

msgpack-c/CMakeLists.txt

Line 308 in 9c45623

IF ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")

However, it seems that the setting doesn't work.

I've checked https://stackoverflow.com/questions/41692725/cmake-doesnt-recognize-msvc-compiler

Maybe we should use

if (CMAKE_CXX_COMPILER_ID MATCHES "MSVC")

I'm not sure which version of cmake starts to support the comparison above. (And it is difficult for me that specifying version that starts to support some functionality)

The current minimal requirement cmake version is 2.8.12.

msgpack-c/CMakeLists.txt

Line 1 in 9c45623

CMAKE_MINIMUM_REQUIRED (VERSION 2.8.12)

I think that it is too old. The blocker was Centos. Centos 7 has cmake 2.8.12. But now, the current stable version of Centos is 8. And it has cmake 3.11.4.

I also checked Debian stable. That is buster and cmake version is 3.13.4.

So I will update the minimal cmake version to 3.11.4 from 2.8.12.
Then fix the MSVC comparison and will fix warnings (as errors).

[redboltz]

I noticed that the original compiler comparison works well.
The reason of ignored warning as error compiler option on MSVC is simply

msgpack-c/test/CMakeLists.txt

Line 99 in 9c45623

IF (CMAKE_CXX_FLAGS MATCHES "/W[0-4] /WX")

invalid match and replace.
So I close #826 and create #827.