Darwin: Use nm/otool from Soong instead of PATH

Soong now exposes the proper paths to NM & OTOOL so that we don't need
to assume that they're in $PATH.

Test: `m PRODUCT-sdk-sdk` on Mac
Change-Id: If0d963832154841d00ced7a6cfa9de5a014af084
diff --git a/core/config.mk b/core/config.mk
index 1320828..6c062a6 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -311,8 +311,8 @@
 
 # Commands to generate .toc file from Darwin dynamic library.
 define _gen_toc_command_for_macho
-$(hide) otool -l $(1) | grep LC_ID_DYLIB -A 5 > $(2)
-$(hide) nm -gP $(1) | cut -f1-2 -d" " | (grep -v U$$ >> $(2) || true)
+$(hide) $(HOST_OTOOL) -l $(1) | grep LC_ID_DYLIB -A 5 > $(2)
+$(hide) $(HOST_NM) -gP $(1) | cut -f1-2 -d" " | (grep -v U$$ >> $(2) || true)
 endef
 
 combo_target := HOST_