Suppress multiple checks for color support

[ralphlange]

Since #79 has been merged, the GHA output (with verbosity mode off) contains blocks of:

 Building dependency BASE in /home/runner/.cache/base-7.0
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  Checking if gcc -x c -E supports -fdiagnostics-color: yes
  In file included from /usr/include/string.h:535,
                   from ../osi/epicsTime.cpp:20:
[...]

Can things be changed so that the color support is only checked once and the result written into the configuration?
Alternatively: Print this line only in verbose mode?