cmake - orion cmake configuration fails when CMAKE_C_COMPILED_ID is n…

…ot set [OI-1869]

## Jira Ticket

https://swift-nav.atlassian.net/browse/OI-1869

## Bug description

orion build fails with

```bash
CMake Error at third_party/orion-engine/third_party/auk/cmake/swift_nav/LanguageStandards.cmake:63 (if):
  if given arguments:

    "STREQUAL" "IAR"

  Unknown arguments specified
Call Stack (most recent call first):
  third_party/orion-engine/third_party/auk/cmake/swift_nav/SwiftTargets.cmake:351 (swift_set_language_standards)
  third_party/orion-engine/third_party/auk/cmake/swift_nav/SwiftTargets.cmake:373 (swift_add_target)
  proto/CMakeLists.txt:29 (swift_add_library)
```

CMake syntax allows using the variable without ${} to simultaneously
check if variable is defined, and variable content.


## Testing

Updated
`third_party/orion-engine/third_party/auk/cmake/swift_nav/LanguageStandards.cmake`
locally with the fix, CMake config runs correctly.

Triggered-By:	cmake	5b65c03ce8154a2a3a9ae06623849257f87d6dd9
Upstream-PR:	http://github.com/swift-nav/cmake/pull/176