Use CPPFLAGS, CFLAGS, and LDFLAGS

[mr-c]

Hello from Debian :-)

[sfiligoi]

@mr-c Why do you need the CCFLAGS and LDFLAGS?
a)
The whole idea of disabling them in test was to make sure things actually worked without any special flags being used.
(i.e. that the shared library was not dependent on the compiler version or compilation flags used)
b)
For the combined Makefile, it is a very thin wrapper that only invokes other shared libraries.
No strong opinions there.

[mr-c]

a) The whole idea of disabling them in test was to make sure things actually worked without any special flags being used. (i.e. that the shared library was not dependent on the compiler version or compilation flags used)
b)

In Debian we can't distinguish regular compilations from test compilations, so it is easier for us to patch in the flag propagation everywhere. I'll remove this part from this PR

[mr-c]

@mr-c Why do you need the CCFLAGS and LDFLAGS?

Debian injects additional flags to harden builds. We check for the presence of those additional flags in the build logs.

https://wiki.debian.org/Hardening