Fix compatibility with GCC 10.

[DDoSolitary]

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GCC 10 defaults to -fno-common, which requires "extern" when defining global variables in headers.

This template was created based on the work of udemy-dl.

[DDoSolitary]

Tests failed unfortunately... I'll take a look later.

[DL6ER]

Tests are all green after restarting the failed ones. There exists a race-collision in the tests leading to false-negative results. I haven't had the time to look at this so far, also because it doesn't happen very often.

[DL6ER]

Thanks for your submission. I'm slightly surprised I forgot this in only one spot :-)

Can I ask you to add

-fno-common

also to this line:

FTL/src/CMakeLists.txt

Line 44 in e1db31d

set(HARDENING_FLAGS "-fstack-protector-strong -Wp,-D_FORTIFY_SOURCE=2 -Wl,-z,relro,-z,now -fexceptions -funwind-tables -fasynchronous-unwind-tables -Wl,-z,defs -Wl,-z,now -Wl,-z,relro")

and add a descriptive comment above like

# -fno-common: Emit globals without explicit initializer from `.bss` to `.data`. This causes GCC to reject multiple definitions of global variables. This is the new default from GCC-10 on.

to enforce this also in the future?

[DDoSolitary]

@DL6ER Done.

[DL6ER]

Thanks, the failing tests should get fixed by #945