[bugfix] linux64 linker (#8468)

only add '-fuse-ld=gold' if gold exists
While we're at it.. use mold, if mold exists

Author: themancalledjakob

libs/openFrameworksCompiled/project/linux64/config.linux64.default.mk

@@ -27,4 +27,8 @@
 
 include $(OF_SHARED_MAKEFILES_PATH)/config.linux.common.mk
 
-PLATFORM_LDFLAGS += -fuse-ld=gold
+ifneq (, $(shell command -v mold))
+ PLATFORM_LDFLAGS += -fuse-ld=mold
+else ifneq (, $(shell command -v gold))
+ PLATFORM_LDFLAGS += -fuse-ld=gold
+endif

libs/openFrameworksCompiled/project/qtcreator/modules/of/helpers.js

@@ -116,6 +116,12 @@ function pkgExists(pkg){
     return pkgconfig.exitCode() === 0;
 }
 
+function commandExists(command) {
+    var commandProcess = new Process();
+    commandProcess.exec('command', ['-v', command]);
+    return commandProcess.exitCode() === 0;
+}
+
 function findLibsRecursive(dir, platform, exclude){
     var ret = []
     if(!File.exists(dir)){

libs/openFrameworksCompiled/project/qtcreator/modules/of/of.qbs

@@ -210,7 +210,9 @@ Module{
                 ldflags = Helpers.pkgconfig(configs, ["--libs-only-L"]);
                 if(platform === "msys2"){
                     ldflags.push("-L"+FileInfo.joinPaths(Helpers.msys2root(),"mingw32/lib"));
-                }else{
+                }else if (Helpers.commandExists("mold")) {
+                    ldflags.push("-fuse-ld=mold");
+                }else if (Helpers.commandExists("gold")) {
                     ldflags.push("-fuse-ld=gold");
                 }
             }else{