Explicitly declare a library dependency of LLVM*Desc to

LLVM*AsmPrinter.

GenLibDeps.pl fails to detect vtable references. As this is the only
referenced symbol from LLVM*Desc to LLVM*AsmPrinter on optimized
builds, the algorithm that creates the list of libraries to be linked
into tools doesn't know about the dependency and sometimes places the
libraries on the wrong order, yielding error messages like this:

../../lib/libLLVMARMDesc.a(ARMMCTargetDesc.cpp.o): In function
`llvm::ARMInstPrinter::ARMInstPrinter(llvm::MCAsmInfo const&)':
ARMMCTargetDesc.cpp:(.text._ZN4llvm14ARMInstPrinterC1ERKNS_9MCAsmInfoE
[llvm::ARMInstPrinter::ARMInstPrinter(llvm::MCAsmInfo
const&)]+0x2a): undefined reference to `vtable for
llvm::ARMInstPrinter'

llvm-svn: 136328