build failure in riscV64

[Andreas Hasenack]

https://launchpad.net/ubuntu/+source/squid/4.12-1ubuntu1/+build/19819774

DiskIO/.libs/libdiskio.a(IpcIoFile.o): in function `std::__atomic_base<bool>::exchange(bool, std::memory_order)':
/usr/include/c++/10/bits/atomic_base.h:443: undefined reference to `__atomic_exchange_1'

Just a wild guess, maybe we should list riscv64 in d/rules here:
ifneq (,$(filter $(DEB_HOST_ARCH), armel m68k mips mipsel powerpc powerpcspe sh4))
    DEB_LDFLAGS_MAINT_APPEND += -latomic
endif

[Amos Jeffries (yadi)]

The upstream patch http://www.squid-cache.org/Versions/v4/changesets/squid-4-f187e5cf415604d4fe839ba57120d846bfa1e672.patch which in includes in Squid-4.12 and later should resolve linking issues with libatomic.

[Amos Jeffries (yadi)]

Oops, missed the build version number.

From the build log I see:

> checking whether linking without -latomic works... yes

A patch adjusting the configure.ac test logic to also check the exchange operator which is missing on riscv64 is the correct way to go. Please submit upstream PR if anyone wants to create and test such a patch.