Use lto_bool_t instead of a raw `bool` (fixup for r262977).

Hopefully this should bring
llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast back to life.

llvm-svn: 262994
diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index df27ba8..44f7bea 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -739,7 +739,7 @@
  *
  * \since LTO_API_VERSION=18
  */
-extern bool lto_module_is_thinlto(lto_module_t mod);
+extern lto_bool_t lto_module_is_thinlto(lto_module_t mod);
 
 /**
  * Adds a symbol to the list of global symbols that must exist in the final