AC_PROG_CC & user supplied CC

[Frank A. Uepping]

The AC_PROG_CC/CXX are searching for a compiler.
Will the found compiler being used to compile the feature tests?
E.g.: does AC_CHECK_HEADER(...) use the compiler determined by AC_PROG_CC?

What about when the user supplies a compiler via `./configure CC=mygcc'; 
is that compiler used instead of the compiler found by AC_PROG_CC/CXX?

If not what can I do to make the macros use the user supplied compiler?

/FAU