some Makefile and hints tinkering

1. remove all window interface bits from compiler.370, and have
   the preceding include files set some variables to control
   the behavior of compiler.370 when it comes to c++.
2. some more common Makefile lines into sys/unix/hints/include/multiw-3.370.
3. make it so you can pass cppregex=1 on the Make command line to build with
   sys/share/cppregex.cpp instead of posixregex.c
4. fix sys/share/cppregex.cpp so that it will build with clang compiler
   (required an additional header include). I don't know if it would have
   worked with g++ without that change. The include can be placed into an #ifdef
   block if there's an issue with the change on other compilers.
5. Anything that needs to compile using c++ (Qt, sys/share/cppregex.cpp) can
   just ensure that CPLUSPLUS_NEEDED Makefile variable is set above the lines
   in compiler.370 to ensure that things get set up for c++. It no longer
   checks specifically for Qt. That is what sys/unix/hints/include/multiw-2.370
   does now.

sys/unix/hints/macOS.370

@@ -19,7 +19,6 @@
 # note: '#-INCLUDE' is not just a comment; multiw-1 contains sections 1 to 2
 #-INCLUDE multiw-1.370
 
-
 ifneq "$(USEMACPORTS)" "1"
 HAVE_HOMEBREW := $(shell expr `which -s brew; echo $$?` = 0)
 endif
@@ -27,55 +26,6 @@ ifneq "$(USEHOMEBREW)" "1"
 HAVE_MACPORTS := $(shell expr `which -s port; echo $$?` = 0)
 endif
 
-# 3. If you set WANT_WIN_QT, you need to
-#  A) set QTDIR either here or in the environment to point to the Qt5
-#     library installation root.  (Qt2, Qt3, Qt4 will not work)
-#  B) set LIBXPM to point to the Xpm library
-ifndef WANT_WIN_QT
-ifdef WANT_WIN_ALL
-WANT_WIN_QT=1
-endif
-ifdef WANT_WIN_QT5
-ifndef WANT_WIN_QT
-WANT_WIN_QT=1
-endif   # not WANT_WIN_QT
-endif   # WANT_WIN_QT5
-ifdef WANT_WIN_QT6
-ifndef WANT_WIN_QT
-WANT_WIN_QT=1
-endif   # not WANT_WIN_QT
-endif   # WANT_WIN_QT6
-endif   # not WANT_WIN_QT
-
-ifdef WANT_WIN_QT
-ifndef WANT_WIN_QT5
-ifndef WANT_WIN_QT6
-WANT_WIN_QT5=1
-endif   # not WANT_WIN_QT6
-endif   # not WANT_WIN_QT5
-#QTDIR=/Developer/Qt
-ifeq "$(HAVE_HOMEBREW)" "1"
-ifdef WANT_WIN_QT5
-# Qt5 installed via homebrew
-QTDIR :=$(shell brew --prefix)/opt/qt@5
-endif   # WANT_WIN_QT5
-ifdef WANT_WIN_QT6
-QTDIR :=$(shell brew --prefix)/opt/qt@6
-endif   # WANT_WIN_QT6
-endif   # HAVE_HOMEBREW
-ifndef QTDIR
-ifeq "$(HAVE_MACPORTS)" "1"
-ifdef WANT_WIN_QT5
-# Qt5 installed via macports
-QTDIR=/opt/local/libexec/qt5
-endif   # WANT_WIN_QT5
-ifdef WANT_WIN_QT6
-QTDIR=/opt/local/libexec/qt6
-endif   # WANT_WIN_QT6
-endif   # HAVE_MACPORTS
-endif   # QTDIR
-endif	# WANT_WIN_QT
-
 ifndef LIBXPM
 LIBXPM= -L/opt/X11/lib -lXpm
 endif
@@ -87,17 +37,6 @@ endif
 # you're reading this in Makefile augmented by hints, that may not be true).
 #
 
-ifeq "$(GIT)" "1"
-ifndef GITSUBMODULES
-GITSUBMODULES=1
-endif
-endif
-ifeq "$(git)" "1"
-ifndef GITSUBMODULES
-GITSUBMODULES=1
-endif
-endif
-
 #-INCLUDE multiw-2.370
 
 # compiler.370 contains compiler detection and adjustments common
@@ -105,7 +44,31 @@ endif
 
 #-INCLUDE compiler.370
 
+ifdef WANT_WIN_QT
+ifeq "$(HAVE_HOMEBREW)" "1"
+ifdef WANT_WIN_QT5
+# Qt5 installed via homebrew
+QTDIR :=$(shell brew --prefix)/opt/qt@5
+endif   # WANT_WIN_QT5
+ifdef WANT_WIN_QT6
+QTDIR :=$(shell brew --prefix)/opt/qt@6
+endif   # WANT_WIN_QT6
+endif   # HAVE_HOMEBREW
+ifndef QTDIR
+ifeq "$(HAVE_MACPORTS)" "1"
+# Qt installed via macports
+ifdef WANT_WIN_QT5
+QTDIR=/opt/local/libexec/qt5
+endif   # WANT_WIN_QT5
+ifdef WANT_WIN_QT6
+QTDIR=/opt/local/libexec/qt6
+endif   # WANT_WIN_QT6
+endif   # HAVE_MACPORTS
+endif   # QTDIR
+endif   # WANT_WIN_QT
+
 # multiw-3.370 must come after compiler.370
+# and after QTDIR is defined
 
 #-INCLUDE multiw-3.370