Offloading not relocatable

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

So, with the patch (probably undesirable) I've posted, I've managed to
configure/make/make install DESTDIR=... the offload compiler and
configure/make/make install DESTDIR=... the host compiler.

Generally gcc is a relocatable package, so appart from perhaps needing to
add LD_LIBRARY_PATH it doesn't matter if the gcc installed tree as whole
lives somewhere else than prefix (DESTDIR=/usr/src/gcc-git/objinst is
what I've been using), one can still use the compiler normally.

But apparently that is not the case with offloading:

/usr/src/gcc-git/objinst/usr/local/bin/gcc -fopenmp -o target-1 target-1.c
collect2: error trying to exec '/usr/local/bin/x86_64-intelmic-linux-gnu-g++': execvp: No such file or directory
lto-wrapper: fatal error: /usr/src/gcc-git/objinst/usr/local/bin/../libexec/gcc/x86_64-unknown-linux-gnu/5.0.0//accel/x86_64-intelmic-linux-gnu/mkoffload terminated with signal 11 [Segmentation fault], core dumped
compilation terminated.
/usr/bin/ld: lto-wrapper failed
collect2: error: ld returned 1 exit status

>From -v dump, that sounds like a bug in mkoffload, which has been found
properly relatively to the gcc driver or whatever.

/usr/src/gcc-git/objinst/usr/local/bin/../libexec/gcc/x86_64-unknown-linux-gnu/5.0.0//accel/x86_64-intelmic-linux-gnu/mkoffload @/tmp/ccS6Q83l
collect2: error trying to exec '/usr/local/bin/x86_64-intelmic-linux-gnu-g++': execvp: No such file or directory
lto-wrapper: fatal error: /usr/src/gcc-git/objinst/usr/local/bin/../libexec/gcc/x86_64-unknown-linux-gnu/5.0.0//accel/x86_64-intelmic-linux-gnu/mkoffload terminated with signal 11 [Segmentation fault], core dumped
compilation terminated.
/usr/bin/ld: lto-wrapper failed
collect2: error: ld returned 1 exit status

So, I'd say that mkoffload should be using similar stuff like the gcc.c
driver uses to find cc1 relative to the location of the gcc binary.

Also, unrelated to that, I've mentioned to Kirill on IRC privately that
it would be nice if the libgomp offloading plugin API/ABI used some
clearly libgomp & offloading related prefix for all the:
get_type
get_num_devices
offload_register
device_init
device_get_table
device_alloc
device_free
device_dev2host
device_host2dev
device_run
symbols that are part of the plugin interface (GOMP_OFFLOAD_*, or whatever
else).

	Jakub