Modernize codebase by replacing NULL with nullptr

Fixes -Wzero-as-null-pointer-constant warning.

Test: m
Bug: 68236239
Change-Id: I5b4123bc6709641315120a191e36cc57541349b2
diff --git a/libc/bionic/legacy_32_bit_support.cpp b/libc/bionic/legacy_32_bit_support.cpp
index ba59e8e..2de1bc7 100644
--- a/libc/bionic/legacy_32_bit_support.cpp
+++ b/libc/bionic/legacy_32_bit_support.cpp
@@ -104,12 +104,12 @@
 
 // There is no getrlimit64 system call, so we need to use prlimit64.
 int getrlimit64(int resource, rlimit64* limits64) {
-  return prlimit64(0, resource, NULL, limits64);
+  return prlimit64(0, resource, nullptr, limits64);
 }
 
 // There is no setrlimit64 system call, so we need to use prlimit64.
 int setrlimit64(int resource, const rlimit64* limits64) {
-  return prlimit64(0, resource, limits64, NULL);
+  return prlimit64(0, resource, limits64, nullptr);
 }
 
 // There is no prlimit system call, so we need to use prlimit64.