Change semantics to add linkerMergeKeep

Author: LunaTheFoxgirl

source/redub/buildapi.d

@@ -498,7 +498,7 @@ private auto save(TRange)(TRange input)
 /**
 *   This version is actually faster than the other one
 */
-ref string[] exclusiveMerge(StringRange)(return scope ref string[] a, StringRange b, scope const string[] excludeFromMerge = null)
+ref string[] exclusiveMerge(StringRange)(return scope ref string[] a, StringRange b, scope const string[] excludeFromMerge = null, scope const string[] alwaysKeep = null)
 {
     import std.algorithm.searching : countUntil;
     import std.array;
@@ -511,6 +511,11 @@ ref string[] exclusiveMerge(StringRange)(return scope ref string[] a, StringRang
     {
         if(bV.length == 0) continue;
         if(countUntil(excludeFromMerge, bV) != -1) continue;
+        else if (countUntil(alwaysKeep, bV) != -1)
+        {
+            app ~= bV;
+            continue outer;
+        }
         else foreach(aV; a)
         {
             if(aV == bV)

source/redub/parsers/base.d

@@ -138,7 +138,7 @@ void addFrameworks(ref BuildRequirements req, JSONStringArray frameworks, ParseC
 }
 void addVersions(ref BuildRequirements req, JSONStringArray vers, ParseConfig c){req.cfg.versions.exclusiveMerge(vers);}
 void addDebugVersions(ref BuildRequirements req, JSONStringArray vers, ParseConfig c){req.cfg.debugVersions.exclusiveMerge(vers);}
-void addLinkFlags(ref BuildRequirements req, JSONStringArray lFlags, ParseConfig c){req.cfg.linkFlags.exclusiveMerge(lFlags, linkerMergeExceptions);}
+void addLinkFlags(ref BuildRequirements req, JSONStringArray lFlags, ParseConfig c){req.cfg.linkFlags.exclusiveMerge(lFlags, null, linkerMergeKeep);}
 void addDflags(ref BuildRequirements req, JSONStringArray dFlags, ParseConfig c){req.cfg.dFlags.exclusiveMerge(dFlags);}
 void addDependency(
     ref BuildRequirements req, 
@@ -215,7 +215,7 @@ void addSubConfiguration(
         req.dependencies[depIndex].subConfiguration = BuildRequirements.Configuration(subConfigurationName, false);
 }
 
-const string[] linkerMergeExceptions = [
+const string[] linkerMergeKeep = [
     "-l",
     "-framework",
     "-L",