Switch back to the BSD exec for now.

Bug: http://b/31091962
Change-Id: Ia155c4aa0d6db7b91d7486433c3c01a841b0e509
diff --git a/libc/Android.bp b/libc/Android.bp
index 4fcd83e..52006a4 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -518,6 +518,7 @@
     name: "libc_openbsd_large_stack",
     defaults: ["libc_defaults"],
     srcs: [
+        "upstream-openbsd/lib/libc/gen/exec.c",
         "upstream-openbsd/lib/libc/stdio/vfprintf.c",
         "upstream-openbsd/lib/libc/stdio/vfwprintf.c",
         "upstream-openbsd/lib/libc/stdio/vfwscanf.c",
@@ -1237,7 +1238,6 @@
         "bionic/error.cpp",
         "bionic/eventfd_read.cpp",
         "bionic/eventfd_write.cpp",
-        "bionic/exec.cpp",
         "bionic/faccessat.cpp",
         "bionic/fchmod.cpp",
         "bionic/fchmodat.cpp",