libsdl2-powerpc: allow building on Tiger

[barracuda156]

Description

No need to revbump, this only adds configure args for 10.4.

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.4.11
Xcode 2.5

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL in commit message?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[barracuda156]

@reneeotten @herbygillot This is safe to merge: it merely allows the port to build on 10.4 ppc. Nothing else affected.
For 10.4 there are no mad patches too, ha-ha, I just turn off some optional components.