Linux missing aligned_alloc

[jeffhammond]

There should be a CMake test for aligned_malloc that causes the following preprocessor logic to drop from Linux into POSIX when it's missing.

I will work on this if it is the only blocking issue for compiling on CentOS 6 systems (using a much newer compiler than the default, obviously).

void *OSUtil::alignedAlloc(size_t Alignment, size_t NumBytes) {
#if defined(SYCL_RT_OS_LINUX) && 0
  return aligned_alloc(Alignment, NumBytes);
#elif defined(SYCL_RT_OS_POSIX_SUPPORT)
  void *Addr = nullptr;
  int ReturnCode = posix_memalign(&Addr, Alignment, NumBytes);
  return (ReturnCode == 0) ? Addr : nullptr;
#elif defined(SYCL_RT_OS_WINDOWS)
  return _aligned_malloc(NumBytes, Alignment);
#endif
}

FAILED: tools/sycl/source/CMakeFiles/sycl_object.dir/detail/os_util.cpp.o 
/opt/gcc/9.2.0/bin/g++-9 -DCL_TARGET_OPENCL_VERSION=220 -DUSE_PI_CUDA -DXPTI_ENABLE_INSTRUMENTATION -DXPTI_STATIC_LIBRARY -D_DEBUG -D_GLIBCXX_ASSERTIONS=1 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Itools/sycl/source -I/tmp/sycl/sycl/source -Iinclude -I/tmp/sycl/llvm/include -I/tmp/sycl/xpti/include -I/tmp/sycl/sycl/include -Itools/sycl/OpenCL/inc -fPIC -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -fdiagnostics-color -ffunction-sections -fdata-sections -Wall -Wextra -Wno-deprecated-declarations -Werror -O3  -UNDEBUG -fvisibility=hidden -fvisibility-inlines-hidden -std=c++14 -MD -MT tools/sycl/source/CMakeFiles/sycl_object.dir/detail/os_util.cpp.o -MF tools/sycl/source/CMakeFiles/sycl_object.dir/detail/os_util.cpp.o.d -o tools/sycl/source/CMakeFiles/sycl_object.dir/detail/os_util.cpp.o -c /tmp/sycl/sycl/source/detail/os_util.cpp
/tmp/sycl/sycl/source/detail/os_util.cpp: In static member function ‘static void* cl::sycl::detail::OSUtil::alignedAlloc(size_t, size_t)’:
/tmp/sycl/sycl/source/detail/os_util.cpp:246:10: error: ‘aligned_alloc’ was not declared in this scope; did you mean ‘alignedAlloc’?
  246 |   return aligned_alloc(Alignment, NumBytes);
      |          ^~~~~~~~~~~~~
      |          alignedAlloc

[jeffhammond]

Resolved by #2655