add musl-clang, a wrapper for system clang installs

musl-clang allows the user to compile musl-powered programs using their
already existent clang install, without the need of a special cross compiler.
it achieves this by wrapping around both the system clang install and the
linker and passing them special flags to re-target musl at runtime.
it does only affect invocations done through the special musl-clang wrapper
script, so that the user setup remains fully intact otherwise.

the clang wrapper consists of the compiler frontend wrapper script,
musl-clang, and the linker wrapper script, ld.musl-clang.
musl-clang makes sure clang invokes ld.musl-clang to link objects; neither
script needs to be in PATH for the wrapper to work.

2 files changed, 86 insertions, 0 deletions

diff --git a/tools/ld.musl-clang.in b/tools/ld.musl-clang.in
new file mode 100644
index 00000000..93763d6b
--- /dev/null
+++ b/tools/ld.musl-clang.in
@@ -0,0 +1,51 @@
+#!/bin/sh
+cc="@CC@"
+libc_lib="@LIBDIR@"
+ldso="@LDSO@"
+cleared=
+shared=
+userlinkdir=
+userlink=
+
+for x ; do
+    test "$cleared" || set -- ; cleared=1
+
+    case "$x" in
+        -L-user-start)
+            userlinkdir=1
+            ;;
+        -L-user-end)
+            userlinkdir=
+            ;;
+        -L*)
+            test "$userlinkdir" && set -- "$@" "$x"
+            ;;
+        -l-user-start)
+            userlink=1
+            ;;
+        -l-user-end)
+            userlink=
+            ;;
+        crtbegin*.o|crtend*.o)
+            set -- "$@" $($cc -print-file-name=$x)
+            ;;
+        -lgcc|-lgcc_eh)
+            file=lib${x#-l}.a
+            set -- "$@" $($cc -print-file-name=$file)
+            ;;
+        -l*)
+            test "$userlink" && set -- "$@" "$x"
+            ;;
+        -shared)
+            shared=1
+            set -- "$@" -shared
+            ;;
+        -sysroot=*|--sysroot=*)
+            ;;
+        *)
+            set -- "$@" "$x"
+            ;;
+    esac
+done
+
+exec $($cc -print-prog-name=ld) -nostdlib "$@" -lc -dynamic-linker "$ldso"
diff --git a/tools/musl-clang.in b/tools/musl-clang.in
new file mode 100644
index 00000000..623de6f6
--- /dev/null
+++ b/tools/musl-clang.in
@@ -0,0 +1,35 @@
+#!/bin/sh
+cc="@CC@"
+libc="@PREFIX@"
+libc_inc="@INCDIR@"
+libc_lib="@LIBDIR@"
+thisdir="`cd "$(dirname "$0")"; pwd`"
+
+# prevent clang from running the linker (and erroring) on no input.
+sflags=
+eflags=
+for x ; do
+    case "$x" in
+        -l*) input=1 ;;
+        *) input= ;;
+    esac
+    if test "$input" ; then
+        sflags="-l-user-start"
+        eflags="-l-user-end"
+        break
+    fi
+done
+
+exec $cc \
+    -B"$thisdir" \
+    -fuse-ld=musl-clang \
+    -static-libgcc \
+    -nostdinc \
+    --sysroot "$libc" \
+    -isystem "$libc_inc" \
+    -L-user-start \
+    $sflags \
+    "$@" \
+    $eflags \
+    -L"$libc_lib" \
+    -L-user-end