Enhancement: Add -gcflags option for statically compiling binary

[Bertie690]

Describe the feature
Currently, there is an -ldflags argument that passes arguments directly to go build during compilation. This would aim to add a parallel for the gcflags build flags setting as well.

What problem does this feature address?
While there are probably other uses out there that I don't know about, the once instance of this that stands out to me is removing compiler optimizations from built code for debugging. Currently, trying to launch a compiled magefile binary using dlv results in often subpar information due to compiler optimizations, and the means of removing said optimizations require passing gcflags arguments.

Additional context
While a separate flag could be made to disable compiler optimizations, this would be a more general-purpose solution.
Another option would be adding a general "build" flag that passes on its arguments directly to go build, though that might pose backwards compatibility issues.

For the record, the debug setup I am using simply has mage handle compiling the binary and dlv run the finished product afterwards.

mage -compile ./magefile-debug
dlv exec magefiles/magefile-debug

In the event this already exists, I will be very sad.