macros: define a %gobuildflags macro
Using the %gobuild macro is fine for a project where the go
code is the only thing being built, and can be built directly
by invoking the Go toolchain from RPM.
In more complex cases though, the Go code is just a small part
of the project and the Go toolchain is invoked by a build
system such as make (possibly automake), or meson. In such a
case we need to be able to tell this build system what flags
to pass to the compiler.
The %gobuildflags macros services this purpose allowing a
RPM spec todo
GOBUILDFLAGS="%gobuildflags" %configure
or
%make GOBUILDFLAGS="%gobuildflags"
Ideally the %gobuild macro would in turn reference the
%gobuildflags macro, but that does not appear possible
given the semantics around quote expansion and escaping
across RPM and shell.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>