libsanitizer/libbacktrace does not respect --disable-werror

https://bugs.gentoo.org/667104
--- a/libsanitizer/libbacktrace/Makefile.am
+++ b/libsanitizer/libbacktrace/Makefile.am
@@ -37,3 +37,3 @@ AM_CPPFLAGS = -I $(top_srcdir)/../include -I $(top_srcdir)/../libgcc \
 WARN_FLAGS = -W -Wall -Wwrite-strings -Wmissing-format-attribute \
-	     -Wcast-qual -Werror
+	     -Wcast-qual
 C_WARN_FLAGS = $(WARN_FLAGS) -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition
--- a/libsanitizer/libbacktrace/Makefile.in
+++ b/libsanitizer/libbacktrace/Makefile.in
@@ -293,3 +293,3 @@ AM_CPPFLAGS = -I $(top_srcdir)/../include -I $(top_srcdir)/../libgcc \
 WARN_FLAGS = -W -Wall -Wwrite-strings -Wmissing-format-attribute \
-	     -Wcast-qual -Werror
+	     -Wcast-qual