Cleanup .gitignore rules for third_party directory

.gitignore

Index: .gitignore
diff --git a/.gitignore b/.gitignore
index e6b0da5a992a16423e0165d1ee9618a084b68b26..21e4bdaf83431710e3a75b3efe80666469a4de68 100644
--- a/.gitignore
+++ b/.gitignore
@@ -61,12 +61,12 @@ shell_g
 /test/test262/harness
 /testing/gmock
 /testing/gtest
-/third_party
+/third_party/*

[Michael Achenbach, 2017/01/16 07:43:04]

This wouldn't be correct, because binutils is also checked in. How about you
reduce lines 64-69 to:

/third_party/*
!/third_party/binutils
!/third_party/inspector_protocol

[targos, 2017/01/16 10:00:31]

binutils only contains a download script and the binutils.tar.bz2.sha1 files. I
guess the rest should stay ignored.

[Michael Achenbach, 2017/01/16 10:48:56]

Not sure if I understand. Currently the only two directories with files checked
in are:
https://chromium.googlesource.com/v8/v8/+/c4a35ed7e831448e1fd2a2ca1f79d5fefae...

So, all directories except these two should be ignored. /third_party/* ignores
all directories and files matching /third_party/*, so also
/third_party/binutils, which therefore (so I think) should have an exception
!/third_party/binutils.

There are also generated/downloaded files withing binutils that probably should
have their own ignore entries, which we lack. Chromium has one:
https://chromium.googlesource.com/chromium/src/+/lkgr/third_party/binutils/.g...

 /third_party/android_tools
 /third_party/cygwin
 /third_party/icu
 /third_party/instrumented_libraries
-/third_party/inspector_protocol
+!/third_party/inspector_protocol
 /third_party/jinja2
 /third_party/llvm
 /third_party/llvm-build
@@ -104,4 +104,4 @@ v8.ignition_dispatches_table.json
 /test/fuzzer/wasm.tar.gz
 /test/fuzzer/wasm_asmjs.tar.gz
 /src/inspector/build/closure-compiler.tar.gz
-/src/inspector/build/closure-compiler
+/src/inspector/build/closure-compiler