PPC: use 64KB ASLR hint on PPC

Change-Id: I2e461f3f7b3abc666ed5dcc3294a14d27ef0fe60
Reviewed-on: https://chromium-review.googlesource.com/1194583Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#55655}

src/base/platform/platform-posix.cc

@@ -248,11 +248,11 @@ void* OS::GetRandomMmapAddr() {
   // Use extra address space to isolate the mmap regions.
   raw_addr += uint64_t{0x400000000000};
 #elif V8_TARGET_BIG_ENDIAN
-  // Big-endian Linux: 44 bits of virtual addressing.
+  // Big-endian Linux: 42 bits of virtual addressing.
   raw_addr &= uint64_t{0x03FFFFFFF000};
 #else
-  // Little-endian Linux: 48 bits of virtual addressing.
-  raw_addr &= uint64_t{0x3FFFFFFFF000};
+  // Little-endian Linux: 46 bits of virtual addressing.
+  raw_addr &= uint64_t{0x3FFFFFFF0000};
 #endif
 #elif V8_TARGET_ARCH_MIPS64
   // We allocate code in 256 MB aligned segments because of optimizations using