GN: Add environment variables for sysroot, toolchain

GN: Add environment variables for sysroot, toolchain

Also accept a map instead of a single path for each so
the toolchain/sysroot can be set per-arch.

R=johnmccutchan@google.com

Committed: https://github.com/dart-lang/sdk/commit/0962a0f6f5a96f9ab3a420a68d3ee755c7ba4d72

[zra, 2017-01-09 20:22:48]

Description was changed from

==========
GN: Add environment variables for sysroot, toolchain
==========

to

==========
GN: Add environment variables for sysroot, toolchain

Also accept a map instead of a single path for each so
the toolchain/sysroot can be set per-arch.
==========

[zra, 2017-01-09 20:23:34]

zra@google.com changed reviewers:
+ whesse@google.com

[zra, 2017-01-09 20:23:35]

This should help with the GN mips cross-build.

[zra, 2017-01-09 21:36:17]

zra@google.com changed reviewers:
+ johnmccutchan@google.com

[Cutch, 2017-01-09 23:36:45]

lgtm

[zra, 2017-01-09 23:53:25]

Description was changed from

==========
GN: Add environment variables for sysroot, toolchain

Also accept a map instead of a single path for each so
the toolchain/sysroot can be set per-arch.
==========

to

==========
GN: Add environment variables for sysroot, toolchain

Also accept a map instead of a single path for each so
the toolchain/sysroot can be set per-arch.

R=johnmccutchan@google.com

Committed:
https://github.com/dart-lang/sdk/commit/0962a0f6f5a96f9ab3a420a68d3ee755c7ba4d72
==========

[zra, 2017-01-09 23:53:26]

Committed patchset #1 (id:1) manually as
0962a0f6f5a96f9ab3a420a68d3ee755c7ba4d72 (presubmit successful).