Refactor Requirement.expand
Allow explicit conversion of requirements to deps

Fixes #19857.
Revert "Remove default_formula from MPIDependency."

This reverts commit 9aaa89dbe832387249ab3ea4e22a8018cc9fe30a.
gfortran 4.8.1

Closes #20178.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
gfortran 4.8.1 bottles
pyside: style
Remove unnecessary use of instance_eval
boost: revert change to icu option

We can't rename options, it breaks upgrades.
boost149: revert change to icu option
libpst: fix option
pyside: fix shiboken dep
grass: use :postgresql dep
fontforge: fix X dep
urweb: use symbol deps for postgres and mysql
lastfmlib: does not build with clang 425