Change in coreboot[master]: xcompile: Remove --rtlib switch from clang CFLAGS

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Change subject: xcompile: Remove --rtlib switch from clang CFLAGS
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Patch Set 2: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/15204/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/59950/ : SUCCESS