-C acg /full/path/to/your/gcc
If you specify only the name and not the path (eg., ``-C alg gcc-4.4'', then ATLAS will search for the named compiler in your PATH variable. The safest approach is to give the full path to the compiler if gcc choice is critical to you. If you want also specify the gfortran to use, additionally add the flag:
-C if /full/path/to/your/gfortran
IMPORTANT NOTE: If you use a different gcc than preferred version, you may reduce performance. Therefore once your build is finished, you should make sure to compare your achieved performance against what ATLAS's architectural defaults achieved. See Section for details on how to do this. If you can tolerate a long install time, you may also want to tell ATLAS not to use the architectural defaults, as described in Section .
R. Clint Whaley 2016-07-28