Use normal install program to install server headers.

Commit a7032690f9 replaced $(INSTALL) with plain "cp" for installing the
server header files. It sped up "make install" significantly, because
the old logic called $(INSTALL) separately for every header file,
whereas plain "cp" could copy all the files in one command. However, we
have long since made it a requirement that $(INSTALL) can also install
multiple files in one command, see commit f1c5247563. Switch back to
$(INSTALL).

Discussion: https://www.postgresql.org/message-id/200503252305.j2PN52m23610%40candle.pha.pa.us
Discussion: https://www.postgresql.org/message-id/2415283.1641852217%40sss.pgh.pa.us

src/include/Makefile

@@ -48,22 +48,15 @@ install: all installdirs
 	$(INSTALL_DATA) utils/errcodes.h '$(DESTDIR)$(includedir_server)/utils'
 	$(INSTALL_DATA) utils/fmgroids.h '$(DESTDIR)$(includedir_server)/utils'
 	$(INSTALL_DATA) utils/fmgrprotos.h '$(DESTDIR)$(includedir_server)/utils'
-# We don't use INSTALL_DATA for performance reasons --- there are a lot of files
-# (in fact, we have to take some pains to avoid overlength shell commands here)
-	cp $(srcdir)/*.h '$(DESTDIR)$(includedir_server)'/
+	$(INSTALL_DATA) $(srcdir)/*.h '$(DESTDIR)$(includedir_server)'
 	for dir in $(SUBDIRS); do \
-	  cp $(srcdir)/$$dir/*.h '$(DESTDIR)$(includedir_server)'/$$dir/ || exit; \
+	  $(INSTALL_DATA) $(srcdir)/$$dir/*.h '$(DESTDIR)$(includedir_server)'/$$dir || exit; \
 	done
 ifeq ($(vpath_build),yes)
 	for file in catalog/schemapg.h catalog/system_fk_info.h catalog/pg_*_d.h parser/gram.h storage/lwlocknames.h utils/probes.h; do \
-	  cp $$file '$(DESTDIR)$(includedir_server)'/$$file || exit; \
+	  $(INSTALL_DATA) $$file '$(DESTDIR)$(includedir_server)'/$$file || exit; \
 	done
 endif
-	cd '$(DESTDIR)$(includedir_server)' && chmod $(INSTALL_DATA_MODE) *.h
-	for dir in $(SUBDIRS); do \
-	  cd '$(DESTDIR)$(includedir_server)'/$$dir || exit; \
-	  chmod $(INSTALL_DATA_MODE) *.h || exit; \
-	done
 
 installdirs:
 	$(MKDIR_P) '$(DESTDIR)$(includedir)/libpq' '$(DESTDIR)$(includedir_internal)/libpq'