[ELF] Merge Symbol::needs* into uint16_t flags. NFC

Split off from D133003 ([ELF] Parallelize relocation scanning) to make its diff smaller.
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 1eb482e..787223b 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -122,7 +122,7 @@
     // field etc) do the same trick as compiler uses to mark microMIPS
     // for CPU - set the less-significant bit.
     if (config->emachine == EM_MIPS && isMicroMips() &&
-        ((sym.stOther & STO_MIPS_MICROMIPS) || sym.needsCopy))
+        ((sym.stOther & STO_MIPS_MICROMIPS) || sym.hasFlag(NEEDS_COPY)))
       va |= 1;
 
     if (d.isTls() && !config->relocatable) {