Add prlimit to LP32.

Bug: http://b/24918750
Change-Id: I0151cd66ccf79a6169610de35bb9c288c0fa4917
diff --git a/libc/bionic/legacy_32_bit_support.cpp b/libc/bionic/legacy_32_bit_support.cpp
index 20d258d..f2bb37d 100644
--- a/libc/bionic/legacy_32_bit_support.cpp
+++ b/libc/bionic/legacy_32_bit_support.cpp
@@ -111,3 +111,22 @@
 int setrlimit64(int resource, const rlimit64* limits64) {
   return prlimit64(0, resource, limits64, NULL);
 }
+
+// There is no prlimit system call, so we need to use prlimit64.
+int prlimit(pid_t pid, int resource, const rlimit* n32, rlimit* o32) {
+  rlimit64 n64;
+  if (n32 != nullptr) {
+    n64.rlim_cur = (n32->rlim_cur == RLIM_INFINITY) ? RLIM64_INFINITY : n32->rlim_cur;
+    n64.rlim_max = (n32->rlim_max == RLIM_INFINITY) ? RLIM64_INFINITY : n32->rlim_max;
+  }
+
+  rlimit64 o64;
+  int result = prlimit64(pid, resource,
+                         (n32 != nullptr) ? &n64 : nullptr,
+                         (o32 != nullptr) ? &o64 : nullptr);
+  if (result != -1 && o32 != nullptr) {
+    o32->rlim_cur = (o64.rlim_cur == RLIM64_INFINITY) ? RLIM_INFINITY : o64.rlim_cur;
+    o32->rlim_max = (o64.rlim_max == RLIM64_INFINITY) ? RLIM_INFINITY : o64.rlim_max;
+  }
+  return result;
+}