Sema: Bind context generic params using the current ConstraintSystem's generic environment instead of the decl's DC.

[jckarter]

Fixes SR-4833.

rdar://problem/32134718

[jckarter]

@swift-ci Please smoke test

[jckarter]

@slavapestov Does this look good?

[slavapestov]

Looks good to me (and for 4.0 branch as well)

[slavapestov]

Looks like this resolved a compiler crasher too -- nice!

[jckarter]

@swift-ci Please smoke test

[jckarter]

@swift-ci Please smoke test

[jckarter]

@ddunbar This llbuild failure on Linux ring a bell?

******************** TEST 'llbuild-unit :: BuildSystem/BuildSystemTests/BuildSystemTaskTests.staleFileRemovalWithManyFiles' FAILED ********************
Note: Google Test filter = BuildSystemTaskTests.staleFileRemovalWithManyFiles
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from BuildSystemTaskTests
[ RUN      ] BuildSystemTaskTests.staleFileRemovalWithManyFiles
/home/buildnode/disk2/workspace/swift-PR-Linux-smoke-test/branch-master/llbuild/unittests/BuildSystem/BuildSystemTaskTests.cpp:732: Failure
Value of: delegate.getMessages()
  Actual: { "commandPreparing(C.1)", "commandStarted(C.1)", "commandFinished(C.1: 0)" }
Expected: std::vector<std::string>({ "commandPreparing(C.1)", "commandStarted(C.1)", "commandFinished(C.1)", })
Which is: { "commandPreparing(C.1)", "commandStarted(C.1)", "commandFinished(C.1)" }
[  FAILED  ] BuildSystemTaskTests.staleFileRemovalWithManyFiles (31 ms)
[----------] 1 test from BuildSystemTaskTests (31 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (31 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] BuildSystemTaskTests.staleFileRemovalWithManyFiles

 1 FAILED TEST

[aciidgh]

The llbuild failure was just fixed by @neonichu in swiftlang/swift-llbuild#175

[ddunbar]

It was overlapped PRs landing, was fixed in swiftlang/swift-llbuild#175

[ddunbar]

@swift-ci please smoke test linux

[jckarter]

Thanks @aciidb0mb3r and @ddunbar!