[lld-macho] Change bitfield types to be identical.

Symbol's subclasses all have an additional bitfield of type uint8_t (RefState enum).
For the bitfields in the same block tomerge, they should be of the same type. (clang/gcc will work, but others like MSVC does not)

Differential Revision: https://reviews.llvm.org/D113040

Author: oontvoo

lld/MachO/Symbols.h

@@ -103,10 +103,10 @@ class Symbol {
 
 public:
   // True if this symbol was referenced by a regular (non-bitcode) object.
-  bool isUsedInRegularObj : 1;
+  uint8_t isUsedInRegularObj : 1;
 
   // True if an undefined or dylib symbol is used from a live section.
-  bool used : 1;
+  uint8_t used : 1;
 };
 
 class Defined : public Symbol {