openh264: use -read_only_relocs suppress in LDFLAGS on macOS <=10.6 i386

[aeiouaeiouaeiouaeiouaeiouaeiou]

Description

https://build.macports.org/builders/ports-10.6_i386-builder/builds/187131/steps/install-port/logs/stdio
I can't really test it, so any help would be appreciated.
OpenBSD ports use a similar flag for i386.

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.6.8 10K549 x86_64
Xcode 4.2 4C199

Verification

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[aeiouaeiouaeiouaeiouaeiouaeiou]

@barracuda156 @fhgwright can test this code please?

[barracuda156]

@aeiouaeiouaeiouaeiouaeiouaeiou I can’t test for i386, but the suggested fix looks safe, I think.