Fix benchmark-tests

1. fix all_benchmarks. Some new benchmarks were added.
2. move some benchmark suites to the right place.
3. add unit test for https://android-review.googlesource.com/c/platform/bionic/+/724785

Test: compile and run bionic-benchmarks-tests on device.
Change-Id: I2b686b51910a422b664f9ea968199f37944039c0
diff --git a/benchmarks/test_suites/test_alignment_onebuf_manual.xml b/benchmarks/test_suites/test_alignment_onebuf_manual.xml
index 97ed5dd..08ef9bd 100644
--- a/benchmarks/test_suites/test_alignment_onebuf_manual.xml
+++ b/benchmarks/test_suites/test_alignment_onebuf_manual.xml
@@ -18,3 +18,13 @@
   <iterations>1</iterations>
   <args>AT_ONEBUF_MANUAL_ALIGN_32_SIZE_4000</args>
 </fn>
+<fn>
+  <name>BM_string_strlen</name>
+  <iterations>1</iterations>
+  <args>AT_ONEBUF_MANUAL_ALIGN_4_SIZE_MEDIUM</args>
+</fn>
+<fn>
+  <name>BM_string_memset</name>
+  <iterations>1</iterations>
+  <args>AT_ONEBUF_MANUAL_ALIGN_32_SIZE_LARGE</args>
+</fn>