Use $(my_prefix)OS instead of HOST_CROSS_OS

The latter is not module-specific and affects all host modules.  Also
remove the check for LOCAL_IS_HOST_MODULE and use  $(my_prefix)OS.

This should be future-proof, where may use different configurations of
cross-compilations across Linux, Darwin, Windows.

Test: m native
Change-Id: I0a6255a8b83960ffb543b593d4a50d963be1de88
diff --git a/core/use_lld_setup.mk b/core/use_lld_setup.mk
index b0386d5..5f0f412 100644
--- a/core/use_lld_setup.mk
+++ b/core/use_lld_setup.mk
@@ -18,14 +18,12 @@
   endif
 endif
 
-ifeq ($(LOCAL_IS_HOST_MODULE),true)
-  # Do not use LLD for Darwin host executables or shared libraries.  See
-  # https://lld.llvm.org/AtomLLD.html for status of lld for Mach-O.
-  ifeq ($(HOST_OS),darwin)
-    my_use_clang_lld := false
-  endif
-  # http://b/110800681 - lld cannot link Android's Windows modules yet.
-  ifeq ($(HOST_CROSS_OS),windows)
-    my_use_clang_lld := false
-  endif
+# Do not use LLD for Darwin host executables or shared libraries.  See
+# https://lld.llvm.org/AtomLLD.html for status of lld for Mach-O.
+ifeq ($($(my_prefix)OS),darwin)
+my_use_clang_lld := false
+endif
+# http://b/110800681 - lld cannot link Android's Windows modules yet.
+ifeq ($($(my_prefix)OS),windows)
+my_use_clang_lld := false
 endif