Fix the order of the ROCm flags

[fwyzard]

Fix the order of the ROCm flags, to allow ROCM_FLAGS to override CXXFLAGS.

[cmsbuild]

A new Pull Request was created by @fwyzard (Andrea Bocci) for branch scramv3.

@cmsbuild, @smuzaffar, @aandvalenzuela, @iarspider can you please review it and eventually sign? Thanks.
@perrotta, @dpiparo, @rappoccio you are the release manager for this.
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[fwyzard]

please test

[smuzaffar]

@fwyzard , this looks safe to me, I can merge it and add the new tag for next IB

[fwyzard]

Thank you !