Log debug elapsed time using 3 decimal places

For flags like -debug-time-function-bodies, this
makes it easier to measure the impact of parsing
functions that take a short amount of time to parse
(less than 0.1ms) but are parsed many times and
therefore add up over the course of the full build.

Author: Ben Asher

lib/Sema/TypeCheckStmt.cpp

@@ -155,7 +155,7 @@ namespace {
       ASTContext &ctx = Function.getAsDeclContext()->getASTContext();
 
       if (ShouldDump) {
-        llvm::errs() << llvm::format("%0.1f", elapsed * 1000) << "ms\t";
+        llvm::errs() << llvm::format("%0.3f", elapsed * 1000) << "ms\t";
         Function.getLoc().print(llvm::errs(), ctx.SourceMgr);
 
         if (auto *AFD = Function.getAbstractFunctionDecl()) {