Fix instances of '#if __LP64__'.

Triggers -Wundef, which is on in -Weverything.

Bug: http://b/31496165
Change-Id: Ib06107073f7dd1d584c19c222d0430da9d35630b
diff --git a/libc/include/link.h b/libc/include/link.h
index f40e7e4..92ecceb 100644
--- a/libc/include/link.h
+++ b/libc/include/link.h
@@ -34,7 +34,7 @@
 
 __BEGIN_DECLS
 
-#if __LP64__
+#if defined(__LP64__)
 #define ElfW(type) Elf64_ ## type
 #else
 #define ElfW(type) Elf32_ ## type
diff --git a/libc/include/stdint.h b/libc/include/stdint.h
index 1cedca1..322a81c 100644
--- a/libc/include/stdint.h
+++ b/libc/include/stdint.h
@@ -39,7 +39,7 @@
 typedef unsigned short __uint16_t;
 typedef int __int32_t;
 typedef unsigned int __uint32_t;
-#if __LP64__
+#if defined(__LP64__)
 typedef long __int64_t;
 typedef unsigned long __uint64_t;
 #else
@@ -47,7 +47,7 @@
 typedef unsigned long long __uint64_t;
 #endif
 
-#if __LP64__
+#if defined(__LP64__)
 typedef long __intptr_t;
 typedef unsigned long __uintptr_t;
 #else
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 13c3269..3b058e8 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -229,7 +229,7 @@
 #include <android/api-level.h>
 
 /* glibc compatibility. */
-#if __LP64__
+#if defined(__LP64__)
 #define __WORDSIZE 64
 #else
 #define __WORDSIZE 32
@@ -278,7 +278,7 @@
 #include <android/versioning.h>
 
 #if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
-#if __LP64__
+#if defined(__LP64__)
 #define __size_mul_overflow(a, b, result) __builtin_umull_overflow(a, b, result)
 #else
 #define __size_mul_overflow(a, b, result) __builtin_umul_overflow(a, b, result)