build: overhaul wrapper script system for multiple wrapper support

this overhauls part of the build system in order to support multiple
toolchain wrapper scripts, as opposed to solely the musl-gcc wrapper as
before. it thereby replaces --enable-gcc-wrapper with --enable-wrapper=...,
which has the options 'auto' (the default, detect whether to use wrappers),
'all' (build and install all wrappers), 'no' (don't build any) and finally
the options named after the individual compiler scripts (currently only
'gcc' is available) to build and install only that wrapper.
the old --enable-gcc-wrapper is removed from --help, but still available.

it also modifies the wrappers to use the C compiler specified to the build
system as 'inner' compiler, when applicable. as wrapper detection works by
probing this compiler, it may not work with any other.

Makefile

@@ -51,6 +51,8 @@ TOOL_LIBS = lib/musl-gcc.specs
 ALL_LIBS = $(CRT_LIBS) $(STATIC_LIBS) $(SHARED_LIBS) $(EMPTY_LIBS) $(TOOL_LIBS)
 ALL_TOOLS = tools/musl-gcc
 
+WRAPCC_GCC = gcc
+
 LDSO_PATHNAME = $(syslibdir)/ld-musl-$(ARCH)$(SUBARCH).so.1
 
 -include config.mak
@@ -155,7 +157,7 @@ lib/musl-gcc.specs: tools/musl-gcc.specs.sh config.mak
 	sh $< "$(includedir)" "$(libdir)" "$(LDSO_PATHNAME)" > $@
 
 tools/musl-gcc: config.mak
-	printf '#!/bin/sh\nexec "$${REALGCC:-gcc}" "$$@" -specs "%s/musl-gcc.specs"\n' "$(libdir)" > $@
+	printf '#!/bin/sh\nexec "$${REALGCC:-$(WRAPCC_GCC)}" "$$@" -specs "%s/musl-gcc.specs"\n' "$(libdir)" > $@
 	chmod +x $@
 
 $(DESTDIR)$(bindir)/%: tools/%

configure

@@ -28,7 +28,7 @@ Optional features:
   --enable-debug          build with debugging information [disabled]
   --enable-warnings       build with recommended warnings flags [disabled]
   --enable-visibility     use global visibility options to optimize PIC [auto]
-  --enable-gcc-wrapper    build musl-gcc toolchain wrapper [auto]
+  --enable-wrapper=...    build given musl toolchain wrapper [auto]
   --disable-shared        inhibit building shared library [enabled]
   --disable-static        inhibit building static library [enabled]
 
@@ -123,6 +123,8 @@ bindir='$(exec_prefix)/bin'
 libdir='$(prefix)/lib'
 includedir='$(prefix)/include'
 syslibdir='/lib'
+tools=
+tool_libs=
 target=
 optimize=auto
 debug=no
@@ -131,6 +133,7 @@ visibility=auto
 shared=auto
 static=yes
 wrapper=auto
+gcc_wrapper=no
 
 for arg ; do
 case "$arg" in
@@ -154,7 +157,11 @@ case "$arg" in
 --disable-warnings|--enable-warnings=no) warnings=no ;;
 --enable-visibility|--enable-visibility=yes) visibility=yes ;;
 --disable-visibility|--enable-visibility=no) visibility=no ;;
---enable-gcc-wrapper|--enable-gcc-wrapper=yes) wrapper=yes ;;
+--enable-wrapper|--enable-wrapper=yes) wrapper=detect ;;
+--enable-wrapper=all) wrapper=yes ; gcc_wrapper=yes ;;
+--enable-wrapper=gcc) wrapper=yes ; gcc_wrapper=yes ;;
+--disable-wrapper|--enable-wrapper=no) wrapper=no ;;
+--enable-gcc-wrapper|--enable-gcc-wrapper=yes) wrapper=yes ; gcc_wrapper=yes ;;
 --disable-gcc-wrapper|--enable-gcc-wrapper=no) wrapper=no ;;
 --enable-*|--disable-*|--with-*|--without-*|--*dir=*|--build=*) ;;
 --host=*|--target=*) target=${arg#*=} ;;
@@ -215,36 +222,44 @@ tryldflag LDFLAGS_TRY -Werror=unknown-warning-option
 tryldflag LDFLAGS_TRY -Werror=unused-command-line-argument
 
 #
-# Need to know if the compiler is gcc to decide whether to build the
-# musl-gcc wrapper, and for critical bug detection in some gcc versions.
+# Need to know if the compiler is gcc or clang to decide which toolchain
+# wrappers to build.
 #
-printf "checking whether compiler is gcc... "
-if fnmatch '*gcc\ version*' "$(LC_ALL=C $CC -v 2>&1)" ; then
-cc_is_gcc=yes
-else
-cc_is_gcc=no
+printf "checking for C compiler family... "
+cc_ver="$(LC_ALL=C $CC -v 2>&1)"
+cc_family=unknown
+if fnmatch '*gcc\ version*' "$cc_ver" ; then
+cc_family=gcc
 fi
-echo "$cc_is_gcc"
+echo "$cc_family"
 
 #
-# Only build musl-gcc wrapper if toolchain does not already target musl
+# Figure out toolchain wrapper to build
 #
+if test "$wrapper" = auto -o "$wrapper" = detect ; then
+printf "checking for toolchain wrapper to build... "
+if test "$cc_family" = gcc ; then
+gcc_wrapper=yes
 if test "$wrapper" = auto ; then
-printf "checking whether to build musl-gcc wrapper... "
-if test "$cc_is_gcc" = yes ; then
-wrapper=yes
 while read line ; do
-case "$line" in */ld-musl-*) wrapper=no ;; esac
+case "$line" in */ld-musl-*) gcc_wrapper=no ;; esac
 done <<EOF
 $($CC -dumpspecs)
 EOF
+fi
+test "$gcc_wrapper" = yes && echo "gcc"
 else
-wrapper=no
+echo "none"
+if test "$wrapper" = detect ; then
+fail "$0: could not find an appropriate toolchain wrapper"
+fi
 fi
-echo "$wrapper"
 fi
 
-
+if test "$gcc_wrapper" = yes ; then
+tools="$tools tools/musl-gcc"
+tool_libs="$tool_libs lib/musl-gcc.specs"
+fi
 
 #
 # Find the target architecture
@@ -580,11 +595,12 @@ LDFLAGS = $LDFLAGS_AUTO $LDFLAGS
 CROSS_COMPILE = $CROSS_COMPILE
 LIBCC = $LIBCC
 OPTIMIZE_GLOBS = $OPTIMIZE_GLOBS
+ALL_TOOLS = $tools
+TOOL_LIBS = $tool_libs
 EOF
 test "x$static" = xno && echo "STATIC_LIBS ="
 test "x$shared" = xno && echo "SHARED_LIBS ="
-test "x$wrapper" = xno && echo "ALL_TOOLS ="
-test "x$wrapper" = xno && echo "TOOL_LIBS ="
+test "x$cc_family" = xgcc && echo 'WRAPCC_GCC = $(CC)'
 exec 1>&3 3>&-
 
 printf "done\n"