[Driver] -static-pie: add -z text

This matches gcc -static-pie. The intention is to prevent dynamic
relocations in read-only segments.

In ld.bfd and gold, -z notext is the default. If text relocations are needed:

* -z notext: allow and emit DF_TEXTREL.
  DF_TEXTREL is not emitted if there is no text relocation.
* -z text: error

In lld, -z text is the default (this change is a no-op).

* -z text: error on text relocations
* -z notext: allow text relocations, and emit DF_TEXTREL no matter whether
  text relocations exist.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D62606

llvm-svn: 362050