We default to -Zi for Windows debug flags, which is for generating debug info
into a PDB file, but clang-cl doesn't actually implement that so -Zi is
an alias for -Z7 in clang-cl:
http://clang.llvm.org/docs/UsersManual.html#id9
sccache has special handling for -Zi because multiple compiles writing
to the same PDB file is not cacheable, so we've always overridden -Zi with -Z7
in CI when using sccache.
Given that everyone should be using clang-cl nowadays and MSVC will no longer
be supported soon, this patch changes the default and removes some PDB
file name flag setting from rules.mk, as well as the no-longer-necessary
overrides from mozconfig.cache.
Differential Revision: https://phabricator.services.mozilla.com/D18264
--HG--
extra : moz-landing-system : lando
8a4288a193