golang: Allow users to specify desired buildflags
For example one could want to build the software with race detector, e.g.
[gowork]
...
buildflags = -race
or if you want to build a plugin for fluent-bit
[gowork]
...
install = your.package.import.path
buildflags = -buildmode=c-shared
and then your package will be installed as shared library into
${gowork:directory}/pkg/`go env GOOS`_`go env GOARCH`/<your.package.import.path>.a
One could pass that location explicitly to fluentd-bit -e ...
or
symlink to it from some .so from global directory of fluent-bit plugins.
Maybe it is not very good to use go install
for building plugins
(instead of go build -o ...
) but we anyway need to have ability to
specify buildflags as a generic feature, hence this patch.