[libc] Add and install ELKS-specific spec file for gcc-ia16

A spec file (https://gcc.gnu.org/onlinedocs/gcc/Spec-Files.html)
contains spec strings, which say how to transform GCC command
line options into program invocations for the actual compiler
passes.

The spec strings for the ELKS platform used to be maintained
under the gcc-ia16 source tree, but I (tkchia) am now moving
them over here into the ELKS tree.  This should make it easier
to tweak ELKS-specific settings for compilation, assembly, &
linking passes, without having to rebuild the whole gcc-ia16
compiler.

elks/r-elks.spec

@@ -0,0 +1,96 @@
+# Copyright (c) 2022 TK Chia
+#
+# The authors hereby grant permission to use, copy, modify, distribute,
+# and license this software and its documentation for any purpose, provided
+# that existing copyright notices are retained in all copies and that this
+# notice is included verbatim in any distributions. No written agreement,
+# license, or royalty fee is required for any of the authorized uses.
+# Modifications to this software may be copyrighted by their authors
+# and need not follow the licensing terms described here, provided that
+# the new terms are clearly indicated on the first page of each file where
+# they apply.
+
+# Spec strings that control how to transform GCC command line options into
+# program invocations for the actual compiler passes.  See the gcc & gccint
+# info files.
+
+# This is used by %(link), defined below.
+*cmodel_long_ld:
+%{mcmodel=*:%*.ld;:small.ld}
+
+# Define this spec string to glom onto any runtime-specific -m... switches
+# that are recognized & handled by this specs file.  Any runtime-specific
+# switches that are not covered by this spec string will result in an error.
+*ia16_impl_rt_switches:
+%{maout} %{maout-total=*} %{maout-chmem=*} %{maout-stack=*} %{maout-heap=*}
+
+# Transformations and checks to apply to the front-end's own command line
+# (DRIVER_SELF_SPECS).
+*self_spec:
+-nostdinc \
+%{mno-segelf:;:-msegelf} \
+%{fuse-ld=*:;:-fuse-ld=gold} \
+%{mno-protected-mode:;:-mprotected-mode} \
+%{mcmodel=*:;:-mcmodel=small} \
+%{maout-total=*:\
+  %{maout-chmem=*:%emay not use both -maout-total= and -maout-chmem=}\
+  %{maout-stack=*:%emay not use both -maout-total= and -maout-stack=}\
+  %{maout-heap=*:%emay not use both -maout-total= and -maout-heap=}} \
+%{maout-chmem=*:\
+  %{maout-stack=*:%emay not use both -maout-chmem= and -maout-stack=}\
+  %{maout-heap=*:%emay not use both -maout-chmem= and -maout-heap=}}
+
+# Assembler options.
+*asm:
+%{msegelf:--32-segelf}
+
+# C preprocessor options.
+#
+# 1) Bruce's C compiler defines either __MSDOS__ or __ELKS__; follow it here.
+#
+# 2) The -isystem stuff is a hack.  When -mr=elks is specified, then, combined
+#    with the -nostdinc above, this hack will (try to) make GCC use the
+#    include files under the -mr=elks multilib directory, rather than the
+#    Newlib include files in the usual locations.
+#
+#     We also need to extend the hack to
+#	* rope in the libgcc include directories --- via `include-fixed' ---
+#	  since elks-libc's headers use libgcc's;
+#	* fall back on the include directories for the default calling
+#	  convention (.../ia16-elf/lib/elkslibc/include/), in case the user
+#	  says e.g. `-mr=elks -mregparmcall' and no include files are
+#	  installed specifically for this calling convention.
+#
+#     Again, this is a hack.  -- tkchia
+*cpp:
++ \
+-D__ELKS__ \
+-isystem include-fixed/../include%s \
+-isystem include-fixed%s \
+-isystem include%s \
+-isystem elkslibc/include%s
+
+# Linker options.
+*link:
+%{!T*:%Telks-%(cmodel_long_ld)} \
+-m i386elks \
+%{maout-total=*:--defsym=_total=%*} \
+%{maout-chmem=*:--defsym=_chmem=%*} \
+%{maout-stack=*:--defsym=_stack=%*} \
+%{maout-heap=*:--defsym=_heap=%*}
+
+# Object file to place at start of link.
+*startfile:
+-l:crt0.o
+
+# Additional step(s) to run after link (POST_LINK_SPEC).
+*post_link:
+%{!mno-post-link:\
+  %:if-exists-else(../lib/../bin/elf2elks%s elf2elks) \
+  %{v} \
+  %{mcmodel=tiny:--tiny} \
+  %{maout-total=*:--total-data %*} \
+  %{maout-chmem=*:--chmem %*} \
+  %{maout-stack=*:--stack %*} \
+  %{maout-heap=*:--heap %*} \
+  %{o*:%*} %{!o*:a.out}}

libc/Makefile

@@ -210,15 +210,18 @@ install uninstall:
 		    $(lastword $(subst ;, ,$(ml)))))'; \
 		$(MAKE) $@)
 	set -e; \
-	dest=$(DESTDIR)/share/misc/elks; \
+	dest1=$(DESTDIR)/share/misc/elks; \
+	dest2=$(DESTDIR)/ia16-elf/lib/rt-specs; \
 	case $@ in \
 	    install) \
-		mkdir -p "$$dest"; \
+		mkdir -p "$$dest1" "$$dest2"; \
 		cp build-ml/$(MAINMULTISUBDIR)/system/call_tab.v \
-		   build-ml/$(MAINMULTISUBDIR)/system/defn_tab.v "$$dest";; \
+		   build-ml/$(MAINMULTISUBDIR)/system/defn_tab.v "$$dest1"; \
+		cp $(TOPDIR)/elks/r-elks.spec "$$dest2";; \
 	    *) \
-		$(RM) "$$dest"/call_tab.v "$$dest"/defn_tab.v; \
-		rmdir -p "$$dest" || true;; \
+		$(RM) "$$dest1"/call_tab.v "$$dest1"/defn_tab.v \
+		      "$$dest2"/r-elks.spec; \
+		rmdir -p "$$dest1" "$$dest2" || true;; \
 	esac
 endif