[Bug driver/36312] should refuse to overwrite input file with output file

[carlos at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36312

carlos at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |carlos at gcc dot gnu.org
         Resolution|FIXED                       |---

--- Comment #15 from carlos at gcc dot gnu.org ---
This breaks glibc builds.

It is a common configure idiom to use /dev/null in both input and output files.

For example:

configure:72: checking for AVX support
configure:78: /home/triegel/local/gcc/bin/gcc -mavx -xc /dev/null -S -o
/dev/null
gcc: fatal error: input file '/dev/null' is the same as output file
compilation terminated.
configure:81: $? = 1
configure:89: result: no

There is no need for a temporary file and it would slow down configure.

I expect that this change will break many more packages in the distribution
builds because of this common idiom.

It would be sufficient if /dev/null were special cased in some way for Linux
configurations.