strip setup hook: Learn about only stripping host/target binaries alone

`dontStrip` is still a catch-all, but `dontStripHost` and
`dontStripTarget` are also now available for finer-grained disabling.

pkgs/build-support/setup-hooks/strip.sh

@@ -3,24 +3,45 @@
 fixupOutputHooks+=(_doStrip)
 
 _doStrip() {
-    if [ -z "$dontStrip" ]; then
+    # We don't bother to strip build platform code because it shouldn't make it
+    # to $out anyways---if it does, that's a bigger problem that a lack of
+    # stripping will help catch.
+    local -ra flags=(dontStripHost dontStripTarget)
+    local -ra stripCmds=(STRIP TARGET_STRIP)
+
+    # Optimization
+    if [[ "$STRIP" == "$TARGET_STRIP" ]]; then
+        dontStripTarget+=1
+    fi
+
+    local i
+    for i in ${!stripCmds[@]}; do
+        local -n flag="${flags[$i]}"
+        local -n stripCmd="${stripCmds[$i]}"
+
+        # `dontStrip` disables them all
+        if [[ "$dontStrip" || "$flag" ]] || ! type -f "$stripCmd" 2>/dev/null
+        then continue; fi
+
         stripDebugList=${stripDebugList:-lib lib32 lib64 libexec bin sbin}
         if [ -n "$stripDebugList" ]; then
-            stripDirs "$stripDebugList" "${stripDebugFlags:--S}"
+            stripDirs "$stripCmd" "$stripDebugList" "${stripDebugFlags:--S}"
         fi
 
         stripAllList=${stripAllList:-}
         if [ -n "$stripAllList" ]; then
-            stripDirs "$stripAllList" "${stripAllFlags:--s}"
+            stripDirs "$stripCmd" "$stripAllList" "${stripAllFlags:--s}"
         fi
-    fi
+    done
 }
 
 stripDirs() {
-    local dirs="$1"
-    local stripFlags="$2"
+    local cmd="$1"
+    local dirs="$2"
+    local stripFlags="$3"
     local dirsNew=
 
+    local d
     for d in ${dirs}; do
         if [ -d "$prefix/$d" ]; then
             dirsNew="${dirsNew} $prefix/$d "
@@ -29,8 +50,8 @@ stripDirs() {
     dirs=${dirsNew}
 
     if [ -n "${dirs}" ]; then
-        header "stripping (with flags $stripFlags) in$dirs"
-        find $dirs -type f -print0 | xargs -0 ${xargsFlags:--r} $STRIP $commonStripFlags $stripFlags 2>/dev/null || true
+        header "stripping (with command $cmd and flags $stripFlags) in$dirs"
+        find $dirs -type f -print0 | xargs -0 ${xargsFlags:--r} $cmd $commonStripFlags $stripFlags 2>/dev/null || true
         stopNest
     fi
 }