Moved link time build options out of compile time options

[speedy-h]

Moved link time build options out of compile time options

Issue
A link time option is set in the compile time options and has no effect, the file is not stripped and remains a larger size.

I ran with cmake version 3.23.1 and compiler GNU 9.4.0

To repeat:

mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make VERBOSE=1
ls -l libisotp.so 
file libisotp.so

Current code:

-rwxr-xr-x 1 xxxxx xxxxx 16800 Feb  9 12:43 libisotp.so
libisotp.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=bb5eaf2d1b5224dc699c21a17cf76d283f06cbef, not stripped

Running after PR change:

-rwxr-xr-x 1 xxxxx xxxxx 14472 Feb  9 12:43 libisotp.so
libisotp.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=5d5c9d947e2c6969e47f7ecae5bf1414d9878751, stripped

The file is smaller and stripped.

No change for the static library build.

Other points to note
The PR used target_link_libraries which is available in cmake version 3.10. If you're happy to move the cmake version up to 3.13, target_link_options may be better.
https://cmake.org/cmake/help/latest/command/target_link_options.html

This issue was originally noticed when compiling with clang (version 13.0.1) which will fail the build with the following error:

[ 50%] Building C object CMakeFiles/isotp.dir/isotp.c.o
clang: error: argument unused during compilation: '-s' [-Werror,-Wunused-command-line-argument]

[speedy-h]

Below is the make output showing th -s option passed during compiling, but not linking which is resolved in this PR. -O2 is passed at compile time, but -O3 is used by cmake when in release build. During compile, the last optimisation level specified is used, -O2. At link only -O3 is present.

[ 50%] Building C object CMakeFiles/isotp.dir/isotp.c.o
/usr/bin/cc -Disotp_EXPORTS -I/home/xxxxx/temp/isotp-c -O3 -DNDEBUG -fPIC -fPIC -Werror -Wall -Wno-unknown-pragmas -O2 -s -MD -MT CMakeFiles/isotp.dir/isotp.c.o -MF CMakeFiles/isotp.dir/isotp.c.o.d -o CMakeFiles/isotp.dir/isotp.c.o -c /home/xxxxx/temp/isotp-c/isotp.c
[100%] Linking C shared library libisotp.so
/usr/local/bin/cmake -E cmake_link_script CMakeFiles/isotp.dir/link.txt --verbose=1
/usr/bin/cc -fPIC -O3 -DNDEBUG -shared -Wl,-soname,libisotp.so -o libisotp.so CMakeFiles/isotp.dir/isotp.c.o 

[SimonCahill]

Hi there!

Thanks for the contribution!
Seems I completely oversaw that.

Changes seem good and workflows pass. LGTM.

I don't have anything to test currently, but as you've not changed any of the logic, I don't see any issues that may arise. I'll merge it with the master branch.