Perform the correct library path substitutions.

Rather than asserting, replace $ORIGIN with the loading image's parent
directory, $LIB with lib or lib64 depending on the loading image's binary
format, and replace $PLATFORM based on the loading image's machine type.

lib/im/elfcomm.c

@@ -100,7 +100,7 @@ ELF_LIBRARY_PATH_VARIABLE_ENTRY ElfLibraryPathVariables[] = {
 
 KSTATUS
 ImpElfOpenWithPathList (
-    PLOADED_IMAGE Parent,
+    PLOADED_IMAGE PathImage,
     PCSTR LibraryName,
     PSTR PathList,
     PIMAGE_FILE_INFORMATION File,
@@ -115,7 +115,9 @@ Routine Description:
 
 Arguments:
 
-    Parent - Supplies a pointer to the image that needs the library.
+    PathImage - Supplies a pointer to the image that owns the path list. This
+        will be the image that needs the library or an ancestor of the image
+        that needs the library.
 
     LibraryName - Supplies the name of the library to load.
 
@@ -192,7 +194,7 @@ Return Value:
                       LibraryLength);
 
         CompletePath[PrefixLength + LibraryLength] = '\0';
-        Status = ImpElfPerformLibraryPathSubstitutions(Parent,
+        Status = ImpElfPerformLibraryPathSubstitutions(PathImage,
                                                        &CompletePath,
                                                        &CompletePathCapacity);
 
@@ -200,7 +202,7 @@ Return Value:
             break;
         }
 
-        Status = ImOpenFile(Parent->SystemContext, CompletePath, File);
+        Status = ImOpenFile(PathImage->SystemContext, CompletePath, File);
         if (KSUCCESS(Status)) {
             break;
         }
@@ -352,7 +354,7 @@ Return Value:
 
 KSTATUS
 ImpElfPerformLibraryPathSubstitutions (
-    PLOADED_IMAGE Image,
+    PLOADED_IMAGE PathImage,
     PSTR *Path,
     PUINTN PathCapacity
     )
@@ -365,8 +367,8 @@ Routine Description:
 
 Arguments:
 
-    Image - Supplies a pointer to the image loading the library (not the
-        library itself obviously, that hasn't been loaded yet).
+    PathImage - Supplies a pointer to the image that owns the library path (not
+        the library itself obviously, that hasn't been loaded yet).
 
     Path - Supplies a pointer that on input contains the complete path. On
         output this will contain the complete path with variables expanded.
@@ -398,6 +400,7 @@ Return Value:
     UINTN RemainderOffset;
     PSTR Replacement;
     UINTN ReplacementLength;
+    PSTR Separator;
     KSTATUS Status;
     UINTN VariableLength;
     UINTN VariableOffset;
@@ -461,24 +464,59 @@ Return Value:
                           Name);
 
         } else {
+            ReplacementLength = 0;
+            switch (Entry->Variable) {
+            case ElfLibraryPathOrigin:
+                Separator = RtlStringFindCharacterRight(PathImage->FileName,
+                                                        '/',
+                                                        -1);
 
-            //
-            // TODO: Get the correct variable values.
-            //
+                if (Separator != NULL) {
+                    Replacement = PathImage->FileName;
+                    ReplacementLength = (UINTN)Separator - (UINTN)Replacement;
 
-            ASSERT(FALSE);
+                } else {
+                    Replacement = ".";
+                }
 
-            switch (Entry->Variable) {
-            case ElfLibraryPathOrigin:
-                Replacement = ".";
                 break;
 
             case ElfLibraryPathLib:
-                Replacement = "lib";
+                if (PathImage->Format == ImageElf64) {
+                    Replacement = "lib64";
+
+                } else {
+                    Replacement = "lib";
+                }
+
                 break;
 
             case ElfLibraryPathPlatform:
-                Replacement = "i386";
+                switch (PathImage->Machine) {
+                case ImageMachineTypeX86:
+                    Replacement = "i686";
+                    break;
+
+                case ImageMachineTypeX64:
+                    Replacement = "x86_64";
+                    break;
+
+                case ImageMachineTypeArm32:
+                    Replacement = "armv7";
+                    break;
+
+                case ImageMachineTypeArm64:
+                    Replacement = "armv8";
+                    break;
+
+                default:
+
+                    ASSERT(FALSE);
+
+                    Replacement = ".";
+                    break;
+                }
+
                 break;
 
             default:
@@ -489,7 +527,9 @@ Return Value:
                 break;
             }
 
-            ReplacementLength = RtlStringLength(Replacement);
+            if (ReplacementLength == 0) {
+                ReplacementLength = RtlStringLength(Replacement);
+            }
 
             //
             // If the replacement is shorter than the original variable, then