For building v8 using gn on aix_ppc64, linux_s390x and linux_ppc64.

build/build_config.h

Index: build/build_config.h
diff --git a/build/build_config.h b/build/build_config.h
index fd5489f6459bedf3045a19cc3887821144a9eef6..a672380b15765967db320068b237156ac82fb632 100644
--- a/build/build_config.h
+++ b/build/build_config.h
@@ -59,6 +59,8 @@
 #define OS_SOLARIS 1
 #elif defined(__QNXNTO__)
 #define OS_QNX 1
+#elif defined(_AIX)
+#define OS_AIX 1
 #else
 #error Please add support for your platform in build/build_config.h
 #endif
@@ -75,10 +77,10 @@
 
 // For access to standard POSIXish features, use OS_POSIX instead of a
 // more specific macro.
-#if defined(OS_MACOSX) || defined(OS_LINUX) || defined(OS_FREEBSD) ||     \
-    defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_SOLARIS) ||   \
-    defined(OS_ANDROID) || defined(OS_OPENBSD) || defined(OS_SOLARIS) ||  \
-    defined(OS_ANDROID) || defined(OS_NACL) || defined(OS_QNX)
+#if defined(OS_AIX) || defined(OS_ANDROID) || defined(OS_FREEBSD) || \
+    defined(OS_LINUX) || defined(OS_MACOSX) || defined(OS_NACL) ||   \
+    defined(OS_NETBSD) || defined(OS_OPENBSD) || defined(OS_QNX) ||  \
+    defined(OS_SOLARIS)
 #define OS_POSIX 1
 #endif
 
@@ -121,21 +123,16 @@
 #define ARCH_CPU_S390 1
 #define ARCH_CPU_31_BITS 1
 #define ARCH_CPU_BIG_ENDIAN 1
-#elif defined(__PPC64__) && defined(__BIG_ENDIAN__)
+#elif (defined(__PPC64__) || defined(__PPC__)) && defined(__BIG_ENDIAN__)
 #define ARCH_CPU_PPC64_FAMILY 1
 #define ARCH_CPU_PPC64 1
 #define ARCH_CPU_64_BITS 1
 #define ARCH_CPU_BIG_ENDIAN 1
-#elif defined(__PPC64__) && defined(__LITTLE_ENDIAN__)
+#elif defined(__PPC64__)
 #define ARCH_CPU_PPC64_FAMILY 1
 #define ARCH_CPU_PPC64 1
 #define ARCH_CPU_64_BITS 1
 #define ARCH_CPU_LITTLE_ENDIAN 1
-#elif defined(__PPC__)
-#define ARCH_CPU_PPC_FAMILY 1
-#define ARCH_CPU_PPC 1
-#define ARCH_CPU_32_BITS 1
-#define ARCH_CPU_BIG_ENDIAN 1
 #elif defined(__ARMEL__)
 #define ARCH_CPU_ARM_FAMILY 1
 #define ARCH_CPU_ARMEL 1