GHC fails to build on versions of Darwin which include `clock_gettime`. On Darwin versions which include `clock_gettime`, the `#ifdef`s are structured to prefer using `clock_gettime` over the mach-specific time functions and structs; however, a couple of places in GetTime.c use the mach functions unconditionally even though the `mach/mach_time.h` header won't be included if `clock_gettime` is available. The attached patch fixes this by checking `HAVE_CLOCK_GETTIME` first before checking if the OS is Darwin. <details><summary>Trac metadata</summary> | Trac field | Value | | ---------------------- | ---------------- | | Version | 8.0.1 | | Type | Bug | | TypeOfFailure | OtherFailure | | Priority | normal | | Resolution | Unresolved | | Component | Compiler | | Test case | | | Differential revisions | | | BlockedBy | | | Related | | | Blocking | | | CC | | | Operating system | Unknown/Multiple | | Architecture | Unknown/Multiple | </details> <!-- {"blocked_by":[],"summary":"RTS GetTime.c is broken on Darwins that include clock_gettime","status":"New","operating_system":"Unknown/Multiple","component":"Compiler","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.0.1","keywords":[],"differentials":[],"test_case":"","architecture":"Unknown/Multiple","cc":[""],"type":"Bug","description":"GHC fails to build on versions of Darwin which include `clock_gettime`.\r\n\r\nOn Darwin versions which include `clock_gettime`, the `#ifdef`s are structured to prefer using `clock_gettime` over the mach-specific time functions and structs; however, a couple of places in GetTime.c use the mach functions unconditionally even though the `mach/mach_time.h` header won't be included if `clock_gettime` is available.\r\n\r\nThe attached patch fixes this by checking `HAVE_CLOCK_GETTIME` first before checking if the OS is Darwin.","type_of_failure":"OtherFailure","blocking":[]} -->