Make strerror(3) and strsignal(3) thread-safe, and add psignal(3) and psiginfo(3).

Change-Id: I426109db25e907980d6cb3a7a695796e45783b78
diff --git a/tests/Android.mk b/tests/Android.mk
index a973341..eef459c 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -22,6 +22,7 @@
     getcwd_test.cpp \
     pthread_test.cpp \
     regex_test.cpp \
+    string_test.cpp \
 
 test_dynamic_ldflags = -Wl,--export-dynamic -Wl,-u,DlSymTestFunction
 test_dynamic_src_files = \