Large memory requirements for 4.2 and 4.3

[Bradley Lucier]

For many years, the default gcc compile options for C code generated  
by Gambit, the Scheme->C compiler, were very simple (-O1 -fschedule- 
insns2 -fno-math-errno -fno-trapping-math) and I didn't have problems  
with gcc's space requirements to compile those files.  (I often ran  
into complexity issues with the algorithms, but people here fixed  
those over the years.

Recently, Marc Feeley used a genetic algorithm to find better compile  
options for Gambit-generated code; he found that performance  
increased by about 30% with more aggressive optimizations (but not  
gcse, yet ;-).

With these new options I can't compile necessary Gambit-generated C  
files on darwin-ppc in 2 GB of space, with or without modulo  
scheduling.  I'm sure that the same thing will happen on other  
architectures for slightly larger files.

I filed

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29374

that gives an example of gcc requiring inordinate (to my mind)  
amounts of memory to compile a program.  Perhaps someone would like  
to look at this PR and give some perspective on the space  
requirements I'm seeing.

Brad