Clean up mkspecs from old, unsupported and untested mkspecs

They have not been tested with Qt 5, not even once to make sure
that the mkspec passes the sanity check.

This removes for OSes:
  HP-UX (running on PA-RISC -- Itanium still supported)
  SGI IRIX
  SCO Unix
  Tru64 Unix
  Unixware

And compilers:
  IBM xlC (Visual Age C++)
  HP aCC compiler (PA-RISC and Itanium)
  PGCC, cxx and kcc on Linux

There were a couple more OSes detected in the configure script that were
lacking even the mkspec. Those have also been removed.

Of those, only hpuxi-acc and aix-xlc have been tested in the last 9
years, though only with Qt 4 and never tried with C++11 support. IRIX
was last tested over 10 years ago and PA-RISC is definitely not
supported due to its lack of atomic operations.

Support for HP-UXi and AIX is now only possible with GCC (assuming GCC
supports those). Support files for Oracle's Sun Studio compiler are left
behind, but its state is unknown.

Change-Id: I7814054a102a407d876ffffd14b69c796b97c972
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

configure

@@ -561,23 +561,12 @@ if [ -z "$PLATFORM" ]; then
         ;;
      AIX:*)
         #PLATFORM=aix-g++
-        #PLATFORM=aix-g++-64
-        PLATFORM=aix-xlc
-        #PLATFORM=aix-xlc-64
-        PLATFORM_NOTES="AIX: aix-g++ aix-g++-64 aix-xlc-64"
+        PLATFORM=aix-g++-64
+        PLATFORM_NOTES="AIX: aix-g++ aix-g++-64"
         ;;
      GNU:*)
         PLATFORM=hurd-g++
         ;;
-     dgux:*)
-        PLATFORM=dgux-g++
-        ;;
-#     DYNIX/ptx:4*)
-#       PLATFORM=dynix-g++
-#       ;;
-     ULTRIX:*)
-        PLATFORM=ultrix-g++
-        ;;
      FreeBSD:*)
         if [ "$(uname -r | cut -d. -f1)" -ge 10 ]; then
             PLATFORM=freebsd-clang
@@ -593,76 +582,29 @@ if [ -z "$PLATFORM" ]; then
      NetBSD:*)
         PLATFORM=netbsd-g++
         ;;
-     BSD/OS:*|BSD/386:*)
-        PLATFORM=bsdi-g++
-        ;;
-     IRIX*:*)
-        #PLATFORM=irix-g++
-        PLATFORM=irix-cc
-        #PLATFORM=irix-cc-64
-        PLATFORM_NOTES="IRIX: irix-g++ irix-cc-64"
-        ;;
      HP-UX:*)
         case "$UNAME_MACHINE" in
             ia64)
-                #PLATFORM=hpuxi-acc-32
-                PLATFORM=hpuxi-acc-64
-                PLATFORM_NOTES="HP-UXi: hpuxi-acc-32"
-            ;;
-            *)
-                #PLATFORM=hpux-g++
-                PLATFORM=hpux-acc
-                #PLATFORM=hpux-acc-64
-                #PLATFORM=hpux-cc
-                #PLATFORM=hpux-acc-o64
-                PLATFORM_NOTES="HP-UX: hpux-g++ hpux-acc-64 hpux-acc-o64"
+                PLATFORM=hpuxi-g++-64
             ;;
         esac
         ;;
-     OSF1:*)
-        #PLATFORM=tru64-g++
-        PLATFORM=tru64-cxx
-        PLATFORM_NOTES="Tru64: tru64-g++"
-        ;;
      Linux:*)
         PLATFORM=linux-g++
-        PLATFORM_NOTES="Linux: linux-clang linux-kcc linux-icc linux-cxx"
+        PLATFORM_NOTES="Linux: linux-clang linux-icc"
         ;;
      SunOS:5*)
-        #PLATFORM=solaris-g++
+        #PLATFORM=solaris-g++-64
         PLATFORM=solaris-cc
         #PLATFORM=solaris-cc64
-        PLATFORM_NOTES="Solaris: solaris-g++ solaris-cc-64"
-        ;;
-     ReliantUNIX-*:*|SINIX-*:*)
-        PLATFORM=reliant-cds
-        #PLATFORM=reliant-cds-64
-        PLATFORM_NOTES="Reliant UNIX: reliant-cds-64"
+        PLATFORM_NOTES="Solaris: solaris-g++-64 solaris-cc-64"
         ;;
      CYGWIN*:*)
         PLATFORM=cygwin-g++
         ;;
      LynxOS*:*)
         PLATFORM=lynxos-g++
         ;;
-     OpenUNIX:*)
-        #PLATFORM=unixware-g++
-        PLATFORM=unixware-cc
-        PLATFORM_NOTES="OpenUNIX: unixware-g++"
-        ;;
-     UnixWare:*)
-        #PLATFORM=unixware-g++
-        PLATFORM=unixware-cc
-        PLATFORM_NOTES="UnixWare: unixware-g++"
-        ;;
-     SCO_SV:*)
-        #PLATFORM=sco-g++
-        PLATFORM=sco-cc
-        PLATFORM_NOTES="SCO OpenServer: sco-g++"
-        ;;
-     UNIX_SV:*)
-        PLATFORM=unixware-g++
-        ;;
      QNX:*)
         PLATFORM=unsupported/qnx-g++
         ;;