pythongh-93744: Remove configure --with-cxx-main option (python#95651)

Remove the "configure --with-cxx-main" build option: it didn't work
for many years. Remove the MAINCC variable from configure and
Makefile.

The MAINCC variable was added by the issue pythongh-42471: commit
0f48d98. Previously, --with-cxx-main
was named --with-cxx.

Keep CXX and LDCXXSHARED variables, even if they are no longer used
by Python build system.

Author: vstinner

Doc/using/configure.rst

@@ -41,12 +41,6 @@ General Options
 
    See :data:`sys.int_info.bits_per_digit <sys.int_info>`.
 
-.. cmdoption:: --with-cxx-main
-.. cmdoption:: --with-cxx-main=COMPILER
-
-   Compile the Python ``main()`` function and link Python executable with C++
-   compiler: ``$CXX``, or *COMPILER* if specified.
-
 .. cmdoption:: --with-suffix=SUFFIX
 
    Set the Python executable suffix to *SUFFIX*.
@@ -721,22 +715,10 @@ Compiler flags
 
    Example: ``gcc -pthread``.
 
-.. envvar:: MAINCC
-
-   C compiler command used to build the ``main()`` function of programs like
-   ``python``.
-
-   Variable set by the :option:`--with-cxx-main` option of the configure
-   script.
-
-   Default: ``$(CC)``.
-
 .. envvar:: CXX
 
    C++ compiler command.
 
-   Used if the :option:`--with-cxx-main` option is used.
-
    Example: ``g++ -pthread``.
 
 .. envvar:: CFLAGS
@@ -854,7 +836,7 @@ Linker flags
 
    Linker command used to build programs like ``python`` and ``_testembed``.
 
-   Default: ``$(PURIFY) $(MAINCC)``.
+   Default: ``$(PURIFY) $(CC)``.
 
 .. envvar:: CONFIGURE_LDFLAGS
 

Makefile.pre.in

@@ -36,7 +36,6 @@ abs_builddir=	@abs_builddir@
 
 CC=		@CC@
 CXX=		@CXX@
-MAINCC=		@MAINCC@
 LINKCC=		@LINKCC@
 AR=		@AR@
 READELF=	@READELF@
@@ -1222,10 +1221,10 @@ Modules/getpath.o: $(srcdir)/Modules/getpath.c Python/frozen_modules/getpath.h M
 		-o $@ $(srcdir)/Modules/getpath.c
 
 Programs/python.o: $(srcdir)/Programs/python.c
-	$(MAINCC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/python.c
+	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/python.c
 
 Programs/_testembed.o: $(srcdir)/Programs/_testembed.c Programs/test_frozenmain.h
-	$(MAINCC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/_testembed.c
+	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/_testembed.c
 
 Modules/_sre/sre.o: $(srcdir)/Modules/_sre/sre.c $(srcdir)/Modules/_sre/sre.h $(srcdir)/Modules/_sre/sre_constants.h $(srcdir)/Modules/_sre/sre_lib.h
 

Misc/NEWS.d/next/Build/2022-08-04-15-29-35.gh-issue-93744.svRuqm.rst

@@ -0,0 +1,3 @@
+Remove the ``configure --with-cxx-main`` build option: it didn't work for
+many years. Remove the ``MAINCC`` variable from ``configure`` and
+``Makefile``. Patch by Victor Stinner.

configure

@@ -865,29 +865,6 @@ rm -f conftest.c conftest.out
 AC_USE_SYSTEM_EXTENSIONS
 
 AC_SUBST(CXX)
-AC_SUBST(MAINCC)
-AC_MSG_CHECKING(for --with-cxx-main=<compiler>)
-AC_ARG_WITH(cxx_main,
-            AS_HELP_STRING([--with-cxx-main@<:@=COMPILER@:>@],
-                           [compile main() and link Python executable with C++ compiler specified in COMPILER (default is $CXX)]),
-[
-
-	case $withval in
-	no)	with_cxx_main=no
-		MAINCC='$(CC)';;
-	yes)	with_cxx_main=yes
-		MAINCC='$(CXX)';;
-	*)	with_cxx_main=yes
-		MAINCC=$withval
-		if test -z "$CXX"
-		then
-			CXX=$withval
-		fi;;
-	esac], [
-	with_cxx_main=no
-	MAINCC='$(CC)'
-])
-AC_MSG_RESULT($with_cxx_main)
 
 preset_cxx="$CXX"
 if test -z "$CXX"
@@ -1358,7 +1335,7 @@ AC_SUBST(LINKCC)
 AC_MSG_CHECKING(LINKCC)
 if test -z "$LINKCC"
 then
-	LINKCC='$(PURIFY) $(MAINCC)'
+	LINKCC='$(PURIFY) $(CC)'
 	case $ac_sys_system in
 	QNX*)
 	   # qcc must be used because the other compilers do not