[patch] refine getenv_spec_function fallback value for undefined variable

[Jeff Law]

On 06/22/2018 10:23 AM, Olivier Hainque wrote:
> Hello,
> 
> getenv_spec_function features code to return a fake
> value for an undefined variable when we know that we
> shouldn't complain about the variable being undefined
> and that the variable value doesn't matter.
> 
> This code is there to prevent errors about undefined
> variables referenced in specs when we're processing for
> mere "--version" on the command line, for example.
> 
> The current code sets the value to the variable name.
> 
> We have a local configuration (for VxWorks, patch coming) where
> %:getenv is used at the beginning of a STARTFILE_PREFIX_SPEC,
> like:
> 
>   #define STARTFILE_PREFIX_SPEC "%:getenv(VSB_DIR /usr/lib/common)"
> 
> Now, for this spec we have a check that the value is an
> absolute path, and gcc --version for this configuration then
> complains with a message like:
> 
>    i586-wrs-vxworks7-gcc: fatal error: system path 'VSB_DIR/usr/lib/common' is not absolute
> 
> This patch fixes this glitch by simply prepending a '/' to
> the fake value returned by getenv_spec_function for acceptable
> undefined variables.
> 
> We have been using this in-house for months with gcc-7 on a wide
> range of targets.
> 
> Bootstrapped and regression tested with mainline on x86_64-linux.
> 
> Ok to commit ?
> 
> Thanks in advance,
> 
> With Kind Regards,
> 
> Olivier
> 
> 2018-06-22  Olivier Hainque  <hainque@adacore.com>
> 
>         * gcc.c (getenv_spec_function): Prepend '/' to value for allowed
>         undefined variables.
> 
OK
jeff