Add various benchmarks.

These are based on ones from system/extras/tests/bionic/.

Change-Id: I7b1ae15a2ca5d1031a6a511d97b88125c1770047
diff --git a/benchmarks/Android.mk b/benchmarks/Android.mk
index f64c108..797ce62 100644
--- a/benchmarks/Android.mk
+++ b/benchmarks/Android.mk
@@ -33,8 +33,12 @@
     benchmark_main.cpp \
     math_benchmark.cpp \
     property_benchmark.cpp \
+    pthread_benchmark.cpp \
+    semaphore_benchmark.cpp \
+    stdio_benchmark.cpp \
     string_benchmark.cpp \
     time_benchmark.cpp \
+    unistd_benchmark.cpp \
 
 # Build benchmarks for the device (with bionic's .so). Run with:
 #   adb shell bionic-benchmarks