configure: treat unrecognized flags as errors on MSVCHEADmaster

This is important for feature checking to work correctly.

It can happen that an unrecognized flag passes the compile test with
only a warning, while failing in preprocessor-only check with an error.
This causes all test_cpp calls to fail and silently produces arguably
broken MSVC builds. Also, all check_* functions don't work as expected,
because they assume the check passed, even though there was a warning.

Additionally, this brings the behavior in line with GCC/Clang based
builds, failing early on unrecognized flags instead of silently
continuing with warnings in the log.

The /options:strict option is available starting in Visual Studio 2022
version 17.0. Because of that, we cannot use check_cflags alone, as it
would add this flag for older MSVC versions and produce warnings. So, we
need to manually perform a version check. A bit of a chicken and egg
problem.

Perform the version check before adding extra flags from the user to
ensure we don't silently fail the preprocessor check due to invalid
flags on older MSVC versions. Note that behavior differs depending on
whether we are compiling or only preprocessing.

This fixes silent different between handling:

`cl.exe -P foo c.c`
    c1: fatal error C1083: Cannot open source file: 'foo': No such file
    or directory

`cl.exe -c foo c.c`
    cl : Command line warning D9024 : unrecognized source file type
    'foo', object file assumed

Where -P fails, while -c throws warnings only. Of course `foo` is
completely bogus here, but depends on the flags or configuration this
may be unsupported argument. Or even some converted path from MSYS when
run inside it. The objective is to always error out instead of silently
hiding this.

Use check_cflags even after the _MSC_FULL_VER check, for non-MSVC
compilers. For example Clang-CL impersonate MSVC, but does not support
-options:strict flag currently.

Signed-off-by: Kacper Michajłow <kasper93@gmail.com>

0 files changed, 0 insertions, 0 deletions