Bug 18140 – experimental allocators, bitmapped_block UB on OSX 64 bits

See https://auto-tester.puremagic.com/show-run.ghtml?projectid=14&runid=2968834&isPull=true. ****** FAIL debug64 std.experimental.allocator.building_blocks.bitmapped_block core.exception.AssertError@std/experimental/allocator/building_blocks/bitmapped_block.d(173): Data must be aligned properly ---------------- 4 test_runner 0x000000011017985b onAssertErrorMsg + 107 5 test_runner 0x0000000110179ab8 _d_assert_msg + 68 6 test_runner 0x000000010fd0d20f pure ref std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock.__ctor(ubyte[]) + 111 7 test_runner 0x000000010fd0d3a3 pure ref std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock.__ctor(ubyte[], uint) + 51 8 test_runner 0x000000010fd0ff3f pure std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock.__unittest_std_experimental_allocator_building_blocks_bitmapped_block_d_53_17().__lambda2() + 103 9 test_runner 0x000000010fd0f6f7 void std.experimental.allocator.common.testAllocator!(std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock.__unittest_std_experimental_allocator_building_blocks_bitmapped_block_d_53_17().__lambda2()).testAllocator() + 39 10 test_runner 0x000000010fd0d002 void std.experimental.allocator.building_blocks.bitmapped_block.BitmappedBlock!(-2uL, 64u, std.experimental.allocator.building_blocks.null_allocator.NullAllocator).BitmappedBlock.__unittest_std_experimental_allocator_building_blocks_bitmapped_block_d_53_17() + 74 11 test_runner 0x000000010fd04cfb void std.experimental.allocator.building_blocks.bitmapped_block.__modtest() + 103 12 test_runner 0x000000010ecaf7d3 void test_runner.doTest(object.ModuleInfo*, ref core.runtime.UnitTestResult) + 99 13 test_runner 0x000000010ecaf6db core.runtime.UnitTestResult test_runner.testModules() + 395 14 test_runner 0x000000010ecaf527 core.runtime.UnitTestResult test_runner.tester() + 31 15 test_runner 0x000000011017a593 runModuleUnitTests + 151 16 test_runner 0x000000011018f2a5 void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll() + 37 17 test_runner 0x000000011018f223 void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).tryExec(scope void delegate()) + 51 18 test_runner 0x000000011018f186 _d_run_main + 814 19 test_runner 0x000000010ecaf3d5 main + 33 20 test_runner 0x000000010ecaf393 start + 51 21 ??? 0x0000000000000001 0x0 + 1

*** Issue 18262 has been marked as a duplicate of this issue. ***

*** Issue 18914 has been marked as a duplicate of this issue. ***

This seems to have been fixed, the autotester is green.