rustc: Correctly pretty-print macro delimiters

[alexcrichton]

This commit updates the Mac_ AST structure to keep track of the delimiters
that it originally had for its invocation. This allows us to faithfully
pretty-print macro invocations not using parentheses (e.g. vec![...]). This in
turn helps procedural macros due to #43081.

Closes #50840

[rust-highfive]

r? @michaelwoerister

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[petrochenkov]

@bors r+

[bors]

📌 Commit ea719ca has been approved by petrochenkov

[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:05:11] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:05:12] tidy error: /checkout/src/libsyntax/parse/parser.rs:2420: line longer than 100 chars
[00:05:13] some tidy checks failed
[00:05:13] 
[00:05:13] 
[00:05:13] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:05:13] 
[00:05:13] 
[00:05:13] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:05:13] Build completed unsuccessfully in 0:02:00
[00:05:13] Build completed unsuccessfully in 0:02:00
[00:05:13] make: *** [tidy] Error 1
[00:05:13] Makefile:79: recipe for target 'tidy' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:00830bc8
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[alexcrichton]

@bors: r=petrochenkov

[bors]

📌 Commit a137d00 has been approved by petrochenkov

[bors]

⌛ Testing commit a137d00 with merge 7426f5c...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: petrochenkov
Pushing 7426f5c to master...