Log Message:
Upgrade rust to version 1.29.2.

Upstream changes:
 * Workaround for an aliasing-related LLVM bug, which caused miscompilation.
 * The rls-preview component on the windows-gnu targets has been restored.

Pkgsrc changes:
 * More commented-out settings for cross builds on NetBSD.
 * Bump bootstrap kit versions to 1.29.2 for powerpc, sparc64
   and earm7hf.  Anyone up for testing for earm7hf?
 * Because the built-in versions of libgit2, libssh2 and curl
   can no longer be built with the pkgsrc-provided headers for
   those packages (due to version skew; the built-in versions
   have been updated to un-released newer code), the buildlink3.mk
   files for those packages have been commented out.
 * Similarly, to avoid using the native pkgsrc host's headers when cross-
   building, the gcc-wrap script has been adjusted to also re-point
   /usr/pkg/include into the destination's root (where those above pacakges
   are not to be installed).
 * Also have the gcc-wrap script deal with "-I dir" style directives,
   and re-point these also into the destination's root.
 * One patch has been integrated upstream, so removed here.