Finish <search.h>.

I'm unable to find a bug, but we've had requests for this internally
once or twice (though I pointed those folks at the STL), and there's
code we build for the host or in our bootloaders that would use this,
and there's reasonable-looking FreeBSD implementation ready and waiting.

Bug: N/A
Test: ran tests
Change-Id: I6ddee4b71bea4c22ed015debd31d3eaac4fcdd35
diff --git a/libc/libc.arm.map b/libc/libc.arm.map
index 31c2a53..5018951 100644
--- a/libc/libc.arm.map
+++ b/libc/libc.arm.map
@@ -1323,6 +1323,12 @@
     __freading; # future
     __fwriting; # future
     getlogin_r; # future
+    hcreate; # future
+    hcreate_r; # future
+    hdestroy; # future
+    hdestroy_r; # future
+    hsearch; # future
+    hsearch_r; # future
     iconv; # future
     iconv_close; # future
     iconv_open; # future