Using $(INSTALL_DATA) and chmod generates errors as the operation
is not permitted. So use plain copy mode and chown/chgrp
in the post-install target.

Index: libgcc/Makefile.in
--- libgcc/Makefile.in.orig
+++ libgcc/Makefile.in
@@ -1080,7 +1080,7 @@ libgcc-extra-parts: $(EXTRA_PARTS)
 	parts="$(EXTRA_PARTS)";					\
 	for file in $$parts; do					\
 	  rm -f $(gcc_objdir)$(MULTISUBDIR)/$$file;		\
-	  $(INSTALL_DATA) $$file $(gcc_objdir)$(MULTISUBDIR)/;	\
+	  install -c $$file $(gcc_objdir)$(MULTISUBDIR)/;	\
 	  case $$file in 					\
 	    *.a)						\
 	      $(RANLIB) $(gcc_objdir)$(MULTISUBDIR)/$$file ;;	\
@@ -1110,7 +1110,7 @@ install-unwind_h-forbuild: unwind.h
 # internal headers are copied by gcc's install.
 install-unwind_h:
 	$(mkinstalldirs) $(DESTDIR)$(libsubdir)/include
-	$(INSTALL_DATA) unwind.h $(DESTDIR)$(libsubdir)/include
+	install -c unwind.h $(DESTDIR)$(libsubdir)/include
 
 all: install-unwind_h-forbuild
 
@@ -1136,7 +1136,7 @@ install-libunwind:
 
 	# NOTE: Maybe this should go into $(inst_libdir), but this
 	# is where the old mklibgcc.in put it.
-	$(INSTALL_DATA) libunwind.a $(DESTDIR)$(inst_slibdir)/
+	install -c libunwind.a $(DESTDIR)$(inst_slibdir)/
 	chmod 644 $(DESTDIR)$(inst_slibdir)/libunwind.a
 	$(RANLIB) $(DESTDIR)$(inst_slibdir)/libunwind.a
 
@@ -1147,7 +1147,7 @@ install-libunwind:
 install-shared:
 	$(mkinstalldirs) $(DESTDIR)$(inst_libdir)
 
-	$(INSTALL_DATA) libgcc_eh.a $(DESTDIR)$(inst_libdir)/
+	install -c libgcc_eh.a $(DESTDIR)$(inst_libdir)/
 	chmod 644 $(DESTDIR)$(inst_libdir)/libgcc_eh.a
 	$(RANLIB) $(DESTDIR)$(inst_libdir)/libgcc_eh.a
 
@@ -1158,17 +1158,15 @@ install-shared:
 install-leaf: $(install-shared) $(install-libunwind)
 	$(mkinstalldirs) $(DESTDIR)$(inst_libdir)
 
-	$(INSTALL_DATA) libgcc.a $(DESTDIR)$(inst_libdir)/
-	chmod 644 $(DESTDIR)$(inst_libdir)/libgcc.a
+	install -c libgcc.a $(DESTDIR)$(inst_libdir)/
 	$(RANLIB) $(DESTDIR)$(inst_libdir)/libgcc.a
-	$(INSTALL_DATA) libgcov.a $(DESTDIR)$(inst_libdir)/
-	chmod 644 $(DESTDIR)$(inst_libdir)/libgcov.a
+	install -c libgcov.a $(DESTDIR)$(inst_libdir)/
 	$(RANLIB) $(DESTDIR)$(inst_libdir)/libgcov.a
 
 	parts="$(INSTALL_PARTS)";				\
 	for file in $$parts; do					\
 	  rm -f $(DESTDIR)$(inst_libdir)/$$file;		\
-	  $(INSTALL_DATA) $$file $(DESTDIR)$(inst_libdir)/;	\
+	  install -c $$file $(DESTDIR)$(inst_libdir)/;	\
 	  case $$file in 					\
 	    *.a)						\
 	      $(RANLIB) $(gcc_objdir)$(MULTISUBDIR)/$$file ;;	\
