[Format] Add format check for throwing negative numbers

Summary:
The code `throw -1;` is currently formatted by clang-format as
`throw - 1;`. This diff adds a fix for this edge case and a test to check
for this in the future.

For context, I am looking into a related bug in the clang-formatting of
coroutine keywords: `co_yield -1;` is also reformatted in this manner
as `co_yield - 1;`. A later diff will add these changes and tests for the
`co_yield` and `co_return` keywords.

Patch by Jonathan Thomas (jonathoma)!

Reviewers: modocache, sammccall, Quuxplusone

Reviewed By: sammccall

Subscribers: cfe-commits

Tags: #clang-format, #clang

Differential Revision: https://reviews.llvm.org/D69144

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@375258 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/TokenAnnotator.cpp

@@ -1757,7 +1757,7 @@ private:
     // Use heuristics to recognize unary operators.
     if (PrevToken->isOneOf(tok::equal, tok::l_paren, tok::comma, tok::l_square,
                            tok::question, tok::colon, tok::kw_return,
-                           tok::kw_case, tok::at, tok::l_brace))
+                           tok::kw_case, tok::at, tok::l_brace, tok::kw_throw))
       return TT_UnaryOperator;
 
     // There can't be two consecutive binary operators.

unittests/Format/FormatTest.cpp

@@ -6912,6 +6912,7 @@ TEST_F(FormatTest, UnderstandsUnaryOperators) {
   verifyFormat("alignof(char);", getGoogleStyle());
 
   verifyFormat("return -1;");
+  verifyFormat("throw -1;");
   verifyFormat("switch (a) {\n"
                "case -1:\n"
                "  break;\n"