Fix CMAKE_COMPILER_IS_GNU{CC,CXX,G77} documentation and usage typos
The documentation of these was confusing, and usage was misspelled in a few places within CMake. Fix both.
Closes: #16297 (closed), #16308 (closed)
The documentation of these was confusing, and usage was misspelled in a few places within CMake. Fix both.
Closes: #16297 (closed), #16308 (closed)