Fix GCC detection in ERTS' Makefiles

[Jean-Sébastien Pédron]

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Hello,

ERTS’ Makefiles check if $(CC) equals to "gcc" to determine if some
options, like optimization flags, should be added to CFLAGS.

Thus, one can’t use an alternate compiler name while still using GCC
(eg. "gcc-4.4" or "/home/user/my-gcc/bin/gcc"). On FreeBSD, the
lang/erlang port (ie. FreeBSD's package of Erlang) is built with CC=cc
and this results in Erlang being awfully slow[1].

I propose a fix for this, described on this article:
http://wiki.github.com/dumbbell/otp/gcc-detection-in-makefiles

The patch is available in my "gcc_detection" branch:
git fetch git://github.com/dumbbell/otp.git gcc_detection

[1] Just for the record, a simple test where a process sends 10,000,000
messages to another one takes 6.8" when Erlang is compiled with "CC=cc"
but takes only 2.7" when Erlang is compiled with "CC=gcc".

- --
Jean-Sébastien Pédron
http://www.dumbbell.fr/

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