Pass absolute HOST_DMD path

Author: dkorpel

ci/run.sh

@@ -128,7 +128,7 @@ test_dmd() {
     fi
 
     $build_path/dmd -g -i -Icompiler/test -release compiler/test/run.d -ofgenerated/run
-    generated/run -j$N --environment MODEL=$MODEL HOST_DMD=$build_path/dmd "${args[@]}"
+    generated/run -j$N --environment MODEL=$MODEL HOST_DMD="$PWD/$build_path/dmd" "${args[@]}"
 }
 
 # build and run druntime unit tests

compiler/test/run.d

@@ -128,6 +128,9 @@ Options:
     }
 
     // allow overwrites from the environment
+    // HOST_DMD must be either a command on PATH (e.g. `dmd`, `ldmd2`) or an
+    // absolute path; it is used to build test-harness code (dshell scripts,
+    // tools) which runs from various working directories.
     hostDMD = environment.get("HOST_DMD", "dmd");
     unitTestRunnerCommand = resultsDir.buildPath("unit_test_runner").exeName;
 
@@ -585,7 +588,7 @@ string[string] getEnvironment()
         env["SEP"] = `\`;
         env["DFLAGS"] = `-I"%s\import" -defaultlib=druntime -debuglib=druntime`.format(druntimePath);
         env["LIB"] = druntimeLibDir ~ ";" ~ environment.get("LIB");
-        env["PHOBOS_DFLAGS"] = `-I"%s\import" -I"%s"`.format(druntimePath, phobosPath);
+        env["PHOBOS_DFLAGS"] = `-I"%s\import" -I"%s" -L/LIBPATH:"%s"`.format(druntimePath, phobosPath, phobosPath);
     }
     else
     {