[RISCV] Consume error from parsing attributes section

[jrtc27]

Summary

We don't consume the error from getBuildAttributes, so an assertions
build crashes with "Program aborted due to an unhandled Error:".
Explicitly consume it like the ARM version in that case.

[MaskRay]

Looks great!

llvm/lib/Object/ELFObjectFile.cpp

SubtargetFeatures ELFObjectFileBase::getRISCVFeatures() const {
 
   if (PlatformFlags & ELF::EF_RISCV_RVC) {
     Features.AddFeature("c");
   }
 
   // Add features according to the ELF attribute section.
   // If there are any unrecognized features, ignore them.
   RISCVAttributeParser Attributes;
-  if (Error E = getBuildAttributes(Attributes))
+  if (Error E = getBuildAttributes(Attributes)) {
+    // TODO Propagate Error.
+    consumeError(std::move(E));
     return Features; // Keep "c" feature if there is one in PlatformFlags.
+  }
 
   Optional<StringRef> Attr = Attributes.getAttributeString(RISCVAttrs::ARCH);
   if (Attr.hasValue()) {
     // The Arch pattern is [rv32|rv64][i|e]version(_[m|a|f|d|c]version)*
     // Version string pattern is (major)p(minor). Major and minor are optional.
     // For example, a version number could be 2p0, 2, or p92.
     StringRef Arch = Attr.getValue();
     if (Arch.consume_front("rv32"))