Ask RPM for its own arch instead of objdump hacks

[gdams]

Applies the same fix described here: docker-library/openjdk#537

[tellison]

Noting that it removes amd64 i386 recognition, which was strange to have as a couple anyway?

[tianon]

Noting that it removes amd64 i386 recognition, which was strange to have as a couple anyway?

That coupling is the raw output from objdump which represents amd64:

$ docker run --rm openjdk:23-oracle objdump --file-headers /usr/bin/objdump | grep architecture
architecture: i386:x86-64, flags 0x00000150:

(so it's not "lost" so much as replaced by the "x86_64" value returned from rpm instead)