Change in coreboot[master]: util/crossgcc: Fix building gcc 6.3.0 with clang

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Change subject: util/crossgcc: Fix building gcc 6.3.0 with clang
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Patch Set 2:

Build Successful

https://qa.coreboot.org/job/coreboot-gerrit/56261/ : SUCCESS

https://qa.coreboot.org/job/coreboot-checkpatch/11857/ : SUCCESS

https://qa.coreboot.org/job/coreboot-toolchain/318/ : SUCCESS