Audit code for LLVM style: single-line if statements with braces

[RichBarton-Arm]

LLVM projects have a de-facto coding style guideline that single line if statements not have braces. F18 does not currently follow this de-facto style.
For example, in include/flang/common/format.h:
if (suppressMessageCascade_) { return; }
This style is not officially part of the LLVM style guide and we suspect that there is a reasonable groundswell of opinion in the LLVM community that it is a bad style point and ought not to be the de-facto standard. We could open this debate on the llvm-dev list and ask the community to reconsider.

Outcomes:

1. We start an RFC on llvm-dev to have the style guide clarified in this regard.
2. The LLVM coding standard is updated with a final decision on this
3. IF the final decision is to make the no braces on single-line if statements style official, change F18 codebase to match.

[sscalpone]

Are we agreed that a single statement if that is not on a single line must use braces?

https://medium.com/@jonathanabrams/single-line-if-statements-2565c62ff492