Remove unreachable from apis in posix terminal compat windows and return 0

[carlokok]

Summary

These apis are called by lldb process launching but the unreachable causes them to fail on Windows. However, they don't have to do anything because Windows has implied support for terminals. This reverts the apis to their old behavior before the change to unreachable.

[carlokok]

This is from 2016; the code doesn't exist anaymore in this form.

[clayborg]

shouldn't these be returning -1 for some of these? Zero usually means no error. You would need to check each unix function and return the right error code for failure.

/lldb/trunk/include/lldb/Host/windows/PosixApi.h

 int strncasecmp(const char *s1, const char *s2, size_t n);
 
 // empty functions
-inline int posix_openpt(int flag) { LLVM_BUILTIN_UNREACHABLE; }
+inline int posix_openpt(int flag) { return 0; }
 
 inline int strerror_r(int errnum, char *buf, size_t buflen) {
-  LLVM_BUILTIN_UNREACHABLE;
+  return 0;
 }
 
-inline int unlockpt(int fd) { LLVM_BUILTIN_UNREACHABLE; }
-inline int grantpt(int fd) { LLVM_BUILTIN_UNREACHABLE; }
-inline char *ptsname(int fd) { LLVM_BUILTIN_UNREACHABLE; }
 
-inline pid_t fork(void) { LLVM_BUILTIN_UNREACHABLE; }
-inline pid_t setsid(void) { LLVM_BUILTIN_UNREACHABLE; }
+inline int unlockpt(int fd) { return 0; }
+inline int grantpt(int fd) { return 0; }
+inline char *ptsname(int fd) { return 0; }
 
+inline pid_t fork(void) { return 0; }
+inline pid_t setsid(void) { return 0; }
 // vsnprintf and snprintf are provided in MSVC 2015 and higher.
 #if _MSC_VER < 1900
 namespace lldb_private {