[dev.link] ensure package path is set when TEXT symbols are created

[dev.link] ensure package path is set when TEXT symbols are created

We're reworking pclntab generation in the linker, and with that we're
moving FuncID generation in to the compiler. Determining the FuncID is
done by a lookup on the package.function name; therefore, we need the
package whenever we make the TEXT symbols.

Change-Id: I805445ffbf2f895f06ce3a91fb09126d012bf86e
Reviewed-on: https://go-review.googlesource.com/c/go/+/245318
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>