Update msbuild integration warnings: Don't warn on /Zi and /X

[thakis]

Summary

We do need to map /Zi to /Z7 explicitly for msbuild as explained in this file, but since /Zi is passed by default and since things transparently work fine with it mapped to /Z7, we shouldn't produce effectively inactionable noise for it.

Also don't warn on /X since clang-cl supports that (since r326357; the risk of duplicating a bunch of clang-cl driver logic here).

[zturner]

Lgtm

[thakis]

339169, thanks!

llvm/tools/msbuild/LLVM.Cpp.Common.targets

<!-- We hook up a target to run every time ClCompile is about to run, the
        then notice this and pass these through to clang-cl.exe.  Clang would of
        course ignore them, but in some cases (such as /Gm), they would generate
        -Wunused-command-line-argument warnings, so it's better if we can just
        strip them from the command line entirely.  This also has the side
        benefit of making command lines shorter which is always nice when trying
        to look at the tool output.
       -->
   <Target Name="BeforeClCompile" BeforeTargets="ClCompile">
-    <!-- Warn on /Zi and /ZI, then map them both to /Z7. -->
-    <Warning Condition="'%(ClCompile.DebugInformationFormat)' == 'ProgramDatabase'"
-             File="@(ClCompile)(0,0)"
-             Text="clang-cl does not support /Zi (Program Database).  The file will be compiled as if /Z7 (C7 Compatible Debug Info) had been passed.  Update the Debug Information Format in project settings to silence this warning."/>
+    <!-- Warn on /ZI, then map to /Z7. /Zi is mapped to /Z7 below too (see comment there), but don't warn on that. -->
     <Warning Condition="'%(ClCompile.DebugInformationFormat)' == 'EditAndContinue'"
              File="@(ClCompile)(0,0)"
            Text="clang-cl does not support /ZI (Program Database for Edit and Continue).  The file will be compiled as if /Z7 (C7 Compatible Debug Info) had been passed.  Update the Debug Information Format in project settings to silence this warning."/>
 
     <!-- Warn if Fiber Safe Optimizations are enabled, and then ignore them. -->
     <Warning Condition="'%(ClCompile.EnableFiberSafeOptimizations)' == 'true'"
              File="@(ClCompile)(0,0)"
              Text="clang-cl does not support fiber safe optimizations (/GT).  Disable this option in compatibility settings to silence this warning."/>
 
     <!-- Warn if Whole Program Optimization is enabled, and then ignore it. -->
     <Warning Condition="'%(ClCompile.WholeProgramOptimization)' == 'true'"
              File="@(ClCompile)(0,0)"
              Text="clang-cl does not support MSVC Link Time Optimization.  Disable this option in compatibility settings to silence this warning."/>
 
-    <!-- Warn if Ignore Standard Include Paths is non-empty, then ignore it. -->
-    <Warning Condition="'%(ClCompile.IgnoreStandardIncludePath)' == 'true'"
-             File="@(ClCompile)(0,0)"
-             Text="clang-cl does not support Ignore Standard Include Path (/X).  Disable this option in compatibility settings to silence this warning."/>
-
     <!-- Warn if Smaller Type Check is enabled, then ignore it.-->
     <Warning Condition="'%(ClCompile.SmallerTypeCheck)' == 'true'"
              File="@(ClCompile)(0,0)"
              Text="clang-cl does not support Smaller Type Check (/RTCc).  Disable this option in compatibility settings to silence this warning."/>
 
     <!-- Warn if Runtime Checks are enabled, then ignore them.-->
     <Warning Condition="'%(ClCompile.BasicRuntimeChecks)' != 'Default'"
              File="@(ClCompile)(0,0)"