[lldb][AIX] Minor AIX specific changes (#132718)

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

AIX build specific changes

Author: DhruvSrivastavaX

lldb/source/Host/CMakeLists.txt

@@ -7,6 +7,10 @@ if (APPLE AND LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY)
   endif()
 endif()
 
+if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
+  add_definitions("-D_ALL_SOURCE")
+endif()
+
 macro(add_host_subdirectory group)
   list(APPEND HOST_SOURCES ${ARGN})
   source_group(${group} FILES ${ARGN})

lldb/source/Host/common/Host.cpp

@@ -19,7 +19,6 @@
 #include <pwd.h>
 #include <spawn.h>
 #include <sys/stat.h>
-#include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
 #endif