Merge LLVM commit c03fdd340356 to fix lang/rust on powerpc

Summary:
Without it building rust fails with:
ld: error: CallSiteSplitting.cpp:(function llvm::SmallVectorImpl<std::1::pair<llvm::BasicBlock*, llvm::SmallVector<std::1::pair<llvm::ICmpInst*, unsigned int>, 2u> > >::operator=(llvm::SmallVectorImpl<std::1::pair<llvm::BasicBlock*, llvm::SmallVector<std::1::pair<llvm::ICmpInst*, unsigned int>, 2u> > >&&): .text._ZN4llvm15SmallVectorImplINSt3__14pairIPNS_10BasicBlockENS_11SmallVectorINS2_IPNS_8ICmpInstEjEELj2EEEEEEaSEOSB_+0xB0): relocation R_PPC_PLTREL24 out of range: -33582208 is not in [-33554432, 33554431]

This will need to be merged to releng/13.1.

Reviewed by: dim
Differential Revision: https://reviews.freebsd.org/D34652
MFC after: 3 days