cc-wrapper: Clean up dynamic linking with x86 multilib

It's better layering to do everything in ld-wrapper. Also, use numeric
comparisons for `relocatable`.

pkgs/build-support/cc-wrapper/cc-wrapper.sh

@@ -61,10 +61,6 @@ while (( "$n" < "$nParams" )); do
         cppInclude=0
     elif [ "${p:0:1}" != - ]; then
         nonFlagArgs=1
-    elif [ "$p" = -m32 ]; then
-        if [ -e @out@/nix-support/dynamic-linker-m32 ]; then
-            NIX_@infixSalt@_LDFLAGS+=" -dynamic-linker $(< @out@/nix-support/dynamic-linker-m32)"
-        fi
     fi
     n+=1
 done

pkgs/build-support/cc-wrapper/ld-wrapper.sh

@@ -67,12 +67,22 @@ fi
 
 extraAfter+=($NIX_@infixSalt@_LDFLAGS_AFTER)
 
+# Three tasks:
+#
+#   1. Find all -L... switches for rpath
+#
+#   2. Find relocatable flag for build id.
+#
+#   3. Choose 32-bit dynamic linker if needed
 declare -a libDirs
 declare -A libs
-relocatable=
+declare -i relocatable=0 link32=0
 
-# Find all -L... switches for rpath, and relocatable flags for build id.
-if [ "$NIX_@infixSalt@_DONT_SET_RPATH" != 1 ] || [ "$NIX_@infixSalt@_SET_BUILD_ID" = 1 ]; then
+if
+    [ "$NIX_@infixSalt@_DONT_SET_RPATH" != 1 ] \
+        || [ "$NIX_@infixSalt@_SET_BUILD_ID" = 1 ] \
+        || [ -e @out@/nix-support/dynamic-linker-m32 ]
+then
     prev=
     # Old bash thinks empty arrays are undefined, ugh.
     for p in \
@@ -87,6 +97,13 @@ if [ "$NIX_@infixSalt@_DONT_SET_RPATH" != 1 ] || [ "$NIX_@infixSalt@_SET_BUILD_I
             -l)
                 libs["lib${p}.so"]=1
                 ;;
+            -m)
+                # Presumably only the last `-m` flag has any effect.
+                case "$p" in
+                    elf_i386) link32=1;;
+                    *)        link32=0;;
+                esac
+                ;;
             -dynamic-linker | -plugin)
                 # Ignore this argument, or it will match *.so and be added to rpath.
                 ;;
@@ -112,6 +129,14 @@ if [ "$NIX_@infixSalt@_DONT_SET_RPATH" != 1 ] || [ "$NIX_@infixSalt@_SET_BUILD_I
     done
 fi
 
+if [ -e "@out@/nix-support/dynamic-linker-m32" ] && (( "$link32" )); then
+    # We have an alternate 32-bit linker and we're producing a 32-bit ELF, let's
+    # use it.
+    extraAfter+=(
+        '-dynamic-linker'
+        "$(< @out@/nix-support/dynamic-linker-m32)"
+    )
+fi
 
 # Add all used dynamic libraries to the rpath.
 if [ "$NIX_@infixSalt@_DONT_SET_RPATH" != 1 ]; then
@@ -154,7 +179,7 @@ fi
 
 # Only add --build-id if this is a final link. FIXME: should build gcc
 # with --enable-linker-build-id instead?
-if [ "$NIX_@infixSalt@_SET_BUILD_ID" = 1 ] && [ ! "$relocatable" ]; then
+if [ "$NIX_@infixSalt@_SET_BUILD_ID" = 1 ] && ! (( "$relocatable" )); then
     extraAfter+=(--build-id)
 fi