Issue python#27490: Merge pgen cross-compile logic from 3.5

Makefile.pre.in

@@ -791,7 +791,7 @@ Python/sysmodule.o: $(srcdir)/Python/sysmodule.c Makefile
 
 $(IO_OBJS): $(IO_H)
 
-$(GRAMMAR_H): $(GRAMMAR_INPUT) $(PGEN)
+$(GRAMMAR_H): $(GRAMMAR_INPUT) @PGEN_DEPENDENCY@
 	@$(MKDIR_P) Include
 	# Avoid copying the file onto itself for an in-tree build
 	if test "$(cross_compiling)" != "yes"; then \

Misc/ACKS

@@ -1131,6 +1131,7 @@ Steven Pemberton
 Bo Peng
 Santiago Peresón
 George Peristerakis
+Thomas Perl
 Mathieu Perreault
 Mark Perrego
 Trevor Perrin

Misc/NEWS

@@ -80,6 +80,9 @@ Windows
 Build
 -----
 
+- Issue #27490: Do not build pgen when cross-compiling.  Patch by Thomas
+  Perl.
+
 - Issue #26662: Set PYTHON_FOR_GEN in configure as the Python program to be
   used for file generation during the build.
 

configure

@@ -740,6 +740,7 @@ UNIVERSALSDK
 CONFIG_ARGS
 SOVERSION
 VERSION
+PGEN_DEPENDENCY
 PYTHON_FOR_BUILD
 PYTHON_FOR_GEN
 host_os
@@ -3050,14 +3051,17 @@ $as_echo_n "checking for python interpreter for cross build... " >&6; }
 $as_echo "$interp" >&6; }
 	PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`:)$(srcdir)/Lib:$(srcdir)/Lib/$(PLATDIR) '$interp
     fi
+    PGEN_DEPENDENCY=''
 elif test "$cross_compiling" = maybe; then
     as_fn_error $? "Cross compiling required --host=HOST-TUPLE and --build=ARCH" "$LINENO" 5
 else
     PYTHON_FOR_BUILD='./$(BUILDPYTHON) -E'
+    PGEN_DEPENDENCY='$(PGEN)'
 fi
 
 
 
+
 if test "$prefix" != "/"; then
     prefix=`echo "$prefix" | sed -e 's/\/$//g'`
 fi

configure.ac

@@ -81,12 +81,15 @@ if test "$cross_compiling" = yes; then
         AC_MSG_RESULT($interp)
 	PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(_PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/`cat pybuilddir.txt`:)$(srcdir)/Lib:$(srcdir)/Lib/$(PLATDIR) '$interp
     fi
+    PGEN_DEPENDENCY=''
 elif test "$cross_compiling" = maybe; then
     AC_MSG_ERROR([Cross compiling required --host=HOST-TUPLE and --build=ARCH])
 else
     PYTHON_FOR_BUILD='./$(BUILDPYTHON) -E'
+    PGEN_DEPENDENCY='$(PGEN)'
 fi
 AC_SUBST(PYTHON_FOR_BUILD)
+AC_SUBST(PGEN_DEPENDENCY)
 
 dnl Ensure that if prefix is specified, it does not end in a slash. If
 dnl it does, we get path names containing '//' which is both ugly and