guix: Re-evaluate fdebug-prefix-map #34414

It could make sense to double check an re-evaluate if this is all right. Original comment follows:

However, some source files are generated and reside in the build tree. So the mapping should be:

-HOST_CFLAGS+=" -fdebug-prefix-map=${DISTSRC}/src=."
+HOST_CFLAGS+=" -fdebug-prefix-map=${DISTSRC}=."

Otherwise, paths become inconsistent and problematic for configuring source remapping in the debugger:

$ gdb ./bitcoin-fa37928536e0/libexec/bitcoin-node
(gdb) break IsRoutable
Breakpoint 1 at 0xb2aa40: file ./netaddress.cpp, line 463.
(gdb) break mp::ProxyClient<ipc::capnp::messages::Init>::construct
Breakpoint 2 at 0x5d82e0: file /distsrc-base/distsrc-fa37928536e0-x86_64-linux-gnu/build/src/ipc/capnp/init.capnp.proxy-client.c++, line 18.

Originally posted by @hebasto in #34281 (review)

I haven't tested this, but I think the issue exists since the cmake migration.

Given that no one reported it, it seems low priority to fix, but it could still make sense to address, because the proposed fix looks simple enough.

@maflcko fixes #34468

Closing for now. Not sure if this is really needed. In any case, let's move discussion to #36708