undocumented M4 environment variable

[EXCOFFIER, Denis \(CS SYSTEMES INFORMATION\)]

Hello,

I use bison-2.3a and discovered that the bison program reacts at the 
environment variable "M4": if it is set, it is supposed to contain a 
replacement program for the compiled-in m4.

This is not indicated in the documentation, and i suggest that it must be. That 
way, third parties (like maintainers of gcc-4.2.0) would find it a bad idea to 
install an environment variable M4="/tmp/.../gcc-4.2.0/missing m4" in the case 
where m4 is not present in the $PATH during the build of gcc-4.2.0. Currently, 
the result is "Broken Pipe", return code 141, no other explanation available.

By the way, i also suggest that you use the environment variable "BISON_M4" 
instead of the very short "M4" for that purpose.

You may find useful to forward this to the gcc-bug list.

Regards.

Denis Excoffier.

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