with structuredAttrs lists will be bash arrays which cannot be exported
which will be a issue with some patches and some wrappers like cc-wrapper
this makes it clearer that NIX_CFLAGS_COMPILE must be a string as lists
in env cause a eval failure
Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:
ld: CMakeFiles/prom.dir/src/prom_process_stat.c.o:(.bss+0x0): multiple definition of
`prom_process_start_time_seconds'; CMakeFiles/prom.dir/src/prom_collector.c.o:(.bss+0x0): first defined here
