I'm writing to report a discrepancy in http://gcc.gnu.org/install/prerequisites.html
I just discovered that if gmp is boot strapped during gcc build and an older m4 exists, when gmp calls flex, it will fail during configure with: checking for flex... flex checking lex output file root... configure: error: cannot find output from flex; giving up I mention this because the prerequisites page specifies m4 as optional if you're just building gcc. m4 appears to have a minimal requirement if gmp is being boot strapped.
