Avoid gyp_chromium failures when vcvarsall.bat was run
Avoid gyp_chromium failures when vcvarsall.bat was run

If you have DEPOT_TOOLS_WIN_TOOLCHAIN=0 and you have run vcvarsall.bat
(VS 2013 or 2015 versions anyway) then "build\gyp_chromium" will fail.
This happens because vcvarsall.bat sets WindowsSDKDir and MSVSVersion.py
expects to find SetEnv.cmd there but no such file exists anywhere in a
recent copy of the Windows SDK. This problem has been a long-standing
issue with external developers, although for a long time it was masked
by a lack of error handling so it showed up as a different cryptic
error.

This change simply checks for the existence of SetEnv.cmd and doesn't
return a reference to a non-existent file. If SetEnv.cmd is truly
obsolete in this context then we could simply remove this code.

BUG=584870
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1681823002 .

msc-/gyp,Phuehvk/gyp,ttyangf/gyp,AWhetter/gyp,ttyangf/gyp,adblockplus/gyp,turbulenz/gyp,turbulenz/gyp,bnoordhuis/gyp,Phuehvk/gyp,msc-/gyp,chromium/gyp,adblockplus/gyp,bnoordhuis/gyp,AWhetter/gyp,adblockplus/gyp,turbulenz/gyp,Phuehvk/gyp,Phuehvk/gyp,bnoordhuis/gyp,turbulenz/gyp,chromium/gyp,msc-/gyp,adblockplus/gyp,AWhetter/gyp,chromium/gyp,bnoordhuis/gyp,msc-/gyp,chromium/gyp,ttyangf/gyp,turbulenz/gyp,adblockplus/gyp,ttyangf/gyp,AWhetter/gyp,bnoordhuis/gyp,msc-/gyp,ttyangf/gyp,Phuehvk/gyp,chromium/gyp,AWhetter/gyp