Compile libphidget22 with -fPIC

[cottsay]

This seems to be unnecessary on some platforms, but for greater compatibility, it's best to specify it explicitly.

Should resolve build failures on the buildfarm for RHEL 8: https://build.ros2.org/view/Rbin_rhel_el864/job/Rbin_rhel_el864__libphidget22__rhel_8_x86_64__binary/

[mintar]

Are you sure it will fix those build failures? I don't see any mention of fPIC there, only cross compiling.

That being said, this PR looks good to me. Even if it maybe doesn't fix that problem, it shouldn't hurt.

@clalancette : Feel free to merge if you agree.

[clalancette]

Honestly, I think something else is going on with that build error. When I try to build libphidget22 by hand in a CentOS 8 container, I can build it just fine without the addition of -fPIC. I'm not sure why that build thinks it is trying to cross-compile, but my guess is that it is something else in the environment that is causing problems.

@cottsay I'm not sure if this is easy to do, but it may be worthwhile to reconfigure that job to spit out the contents of config.log after it fails to see what it thinks the problem is.

[cottsay]

...spit out the contents of config.log after it fails...

configure:3289: checking whether we are cross compiling
configure:3297: gcc -o conftest -g -O2 -Wno-incompatible-pointer-types -Wno-deprecated-declarations -Wno-format-truncation  -Wl,-z,relro  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld conftest.c  >&5
/bin/ld: /tmp/ccKF3OWt.o: relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a PIE object; recompile with -fPIC
/bin/ld: final link failed: Nonrepresentable section on output
collect2: error: ld returned 1 exit status
configure:3301: $? = 1
configure:3308: ./conftest
/home/mockbuild/rpmbuild/BUILD/ros-rolling-libphidget22-2.0.2/obj-x86_64-redhat-linux-gnu/libphidget22-src/configure: line 3310: ./conftest: No such file or directory
configure:3312: $? = 127
configure:3319: error: in `/home/mockbuild/rpmbuild/BUILD/ros-rolling-libphidget22-2.0.2/obj-x86_64-redhat-linux-gnu/EP_libphidget22-prefix/src/EP_libphidget22-build':
configure:3321: error: cannot run C compiled programs.
If you meant to cross compile, use `--host'.

The problem is that the CMakeLists.txt is overriding CFLAGS but not LDFLAGS. So the RPM build process sets the platform's standard CFLAGS and LDFLAGS, and it turns out that some of the LDFLAGS depend on the CFLAGS (-fPIC, namely).

This problem could also be solved by appending to the CFLAGS instead of overriding them, or by overriding the LDFLAGS with an empty value.

This change seemed like the easiest pitch.

[clalancette]

Ah, I see. Makes sense, thanks for the explanation. Looks good to me then.

[clalancette]

@mintar Do you mind doing a source and bloom release into Foxy and Rolling with this change? Or I can do it if you don't have time. Thanks.

[mintar]

I'm on vacation at the moment, so it would be great if you could do it. In general I think it would be good if you'd do the ROS2 releases, merge PRs etc., and I'll do it for ROS1 if you agree.

[clalancette]

I'm on vacation at the moment, so it would be great if you could do it. In general I think it would be good if you'd do the ROS2 releases, merge PRs etc., and I'll do it for ROS1 if you agree.

Sounds good to me, thank you!