[lldb][AIX] Some base #if _AIX changes of a minimal lldb build (#120979)

This PR is in reference to porting LLDB on AIX.

Link to discussions on llvm discourse and github:

1. https://discourse.llvm.org/t/port-lldb-to-ibm-aix/80640
2. #101657
The complete changes for porting are present in this draft PR:
#102601

Added some base #if _AIX changes for minimal lldb build.
Added a PR for clang-format changes separately, to rebase this on later:

- #120978

Review Request: @labath @DavidSpickett

Author: DhruvSrivastavaX

lldb/source/Host/posix/ConnectionFileDescriptorPosix.cpp

@@ -730,9 +730,19 @@ ConnectionStatus ConnectionFileDescriptor::ConnectFile(
     struct termios options;
     ::tcgetattr(fd, &options);
 
-    // Set port speed to maximum
+    // Set port speed to the available maximum
+#ifdef B115200
     ::cfsetospeed(&options, B115200);
     ::cfsetispeed(&options, B115200);
+#elif B57600
+    ::cfsetospeed(&options, B57600);
+    ::cfsetispeed(&options, B57600);
+#elif B38400
+    ::cfsetospeed(&options, B38400);
+    ::cfsetispeed(&options, B38400);
+#else
+#error "Maximum Baud rate is Unknown"
+#endif
 
     // Raw input, disable echo and signals
     options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);

lldb/source/Plugins/Language/ObjC/Cocoa.cpp

@@ -1226,7 +1226,7 @@ bool lldb_private::formatters::ObjCSELSummaryProvider(
 time_t lldb_private::formatters::GetOSXEpoch() {
   static time_t epoch = 0;
   if (!epoch) {
-#ifndef _WIN32
+#if !defined(_WIN32) && !defined(_AIX)
     tzset();
     tm tm_epoch;
     tm_epoch.tm_sec = 0;

lldb/source/Plugins/ObjectContainer/BSD-Archive/ObjectContainerBSDArchive.cpp

@@ -8,7 +8,7 @@
 
 #include "ObjectContainerBSDArchive.h"
 
-#if defined(_WIN32) || defined(__ANDROID__)
+#if defined(_WIN32) || defined(__ANDROID__) || defined(_AIX)
 // Defines from ar, missing on Windows
 #define SARMAG 8
 #define ARFMAG "`\n"