[libc][Obvious] Bump hermetic alloc space to 64KB.

Few hermetic tests are failing as they are running out of memory.

Differential Revision: https://reviews.llvm.org/D150724

Author: Siva Chandra Reddy

libc/test/UnitTest/HermeticTestUtils.cpp

@@ -29,7 +29,7 @@ namespace {
 // requires. Hence, as a work around for this problem, we use a simple allocator
 // which just hands out continuous blocks from a statically allocated chunk of
 // memory.
-static constexpr uint64_t MEMORY_SIZE = 16384;
+static constexpr uint64_t MEMORY_SIZE = 65336;
 static uint8_t memory[MEMORY_SIZE];
 static uint8_t *ptr = memory;