Error on install (during build) with long path on Windows #152

I don't know that all the details of the steps to reproduce are important (exact source of emsdk, the build tool I used, the exact command line options the build tool passed). I know that when I followed the same steps and used a more shallow directory that the install command built and succeeded.

The instructions to repro exactly:

1. Setup build environment (Windows box)
2. Clone/unzip source (I got emsdk-portable from "mozilla games" pacakge, via the "fips" build tool for the "sokol-samples" project)
3. (2a) Use a somewhat long path (in my case, was effectively C:\Users\my_user_name\development\fips-sdks\win\emsdk-portable)
4. emsdk.bat update
5. emsdk.bat install --shallow --disable-assertions sdk-incoming-64bit

Expected: Build/install completes, or some sort of early warning system goes off saying the path is going to be too long
Actual: Build/install fails with hard to debug error:

C:\Program Files (x86)\MSBuild\Microsoft.Cpp\v4.0\V140\Microsoft.CppBuild.targets(312,5): error MSB3491: Could not write lines to file "x64\Release\ClangAttrSubMatchRulesParserStringSwitches\ClangAtt.8917E2BC.tlog\ClangAttrSubMatchRulesParserStringSwitches.lastbuildstate". The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters. [C:\Users\my_user_name\development\fips-sdks\win\emsdk-portable\clang\fastcomp\build_incoming_vs2015_64\tools\clang\include\clang\Parse\ClangAttrSubMatchRulesParserStringSwitches.vcxproj]