compiler: resolve importing ambiguity for more complex function calls

compiler: resolve importing ambiguity for more complex function calls

    Tweak the exporter for inlinable function bodies to work around a
    problem with importing of function calls whose function expressions
    are not simple function names. In the bug in question, the function
    body exporter was writing out a function call of the form

           (*(*FuncTyp)(var))(arg)

    which produced an export data representation of

           *$convert(<type 5>, var)(x)

    which is hard to parse unambiguously. Fix: change the export data
    emitter to introduce parens around the function expression for more
    complex calls.

    Testcase for this bug is in CL 197217.

    Fixes golang/go#34503.

    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/197122

From-SVN: r276228