[mbedtls] update to 'https://github.com/nestlabs/nlbuild-autotools.git' tag '1.6.16'.

third_party/nlbuild-autotools/repo/.default-version

@@ -1 +1 @@
-1.6.14
+1.6.16

third_party/nlbuild-autotools/repo/CHANGES

@@ -1,3 +1,7 @@
+1.6.16 (2020-01-23)
+
+        * Allow absolute paths in PRETTY_FILES.
+
 1.6.15 (2019-12-06)
 
         * Remove redundant libtool m4 libraries.

third_party/nlbuild-autotools/repo/automake/post/rules/pretty.am

@@ -47,8 +47,8 @@
 define nl-make-pretty
 $(AM_V_at)for file in $(4); do \
     $(1) \
-    if test -f $${file}; then d=.; else d=$(srcdir); fi; \
-    $(2) $(3) $${d}/$${file} \
+    if test -f $${file}; then d=; else d=$(srcdir)/; fi; \
+    $(2) $(3) $${d}$${file} \
     || exit 1; \
 done
 endef