Set -Cpanic=abort in windows-msvc stack protector tests

[saethlin]

I ran into a test failure with the 32-bit windows test on #117192, one of the tests has been incorrectly passing (until my change!) because it is picking up the stack protector from another function. I've tried to prevent that happening again by adding CHECK-DAGs for the start and end of each function.

I've also done my best to correct the comments, some were based on the fact that we used to run these tests with unwinding panics, but LLVM doesn't add protectors to function with SEH funclets so it's must more straightforward for these tests to use -Cpanic=abort.

[saethlin]

@bors try jobs=i686-msvc-1,i686-msvc-2,x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

💔 Test for 2c131d9 failed: CI. Failed jobs:

• try - x86_64-msvc-2 (web logs, extended logs)

[saethlin]

@bors try jobs=i686-msvc-1,i686-msvc-2,x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

💔 Test for 4f07087 failed: CI. Failed jobs:

• try - x86_64-msvc-1 (web logs, extended logs)

[saethlin]

@bors try jobs=i686-msvc-1,i686-msvc-2,x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

💔 Test for b651f78 failed: CI. Failed jobs:

• try - x86_64-msvc-1 (web logs, extended logs)

[saethlin]

@bors try jobs=i686-msvc-1,i686-msvc-2,x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

💔 Test for 730886e failed: CI. Failed jobs:

• try - i686-msvc-1 (web logs, extended logs)

[saethlin]

@bors try jobs=i686-msvc-1,i686-msvc-2,x86_64-msvc-1,x86_64-msvc-2

[rust-bors]

☀️ Try build successful (CI)
Build commit: 656f997 (656f997dca95117bdd725db6239552897670cc6b, parent: 503dce33e2e2a5d2fe978b2723ab2a994cc27472)