add some documentation

test/Makefile

@@ -38,6 +38,8 @@
 #
 #   REQUIRED_ARGS:       arguments to add to the $(DMD) command line
 #                        default: (none)
+#                        note: the make variable REQUIRED_ARGS is also added to the $(DMD) 
+#                              command line (see below)
 #
 #   DISABLED:            text describing why the test is disabled (if empty, the test is
 #                        considered to be enabled).
@@ -77,6 +79,7 @@ endif
 QUIET=@
 export RESULTS_DIR=test_results
 export MODEL=32
+export REQUIRED_ARGS=
 
 ifeq ($(OS),win32)
 export ARGS=-inline -release -g -O -unittest

test/d_do_test.d

@@ -24,15 +24,16 @@ void usage()
           "   example: d_do_test runnable pi d\n"
           "\n"
           "   relevant environment variables:\n"
-          "      ARGS:        set to execute all combinations of\n"
-          "      DMD:         compiler to use, ex: ../src/dmd\n"
-          "      OS:          win32, linux, freebsd, osx\n"
-          "      RESULTS_DIR: base directory for test results\n"
+          "      ARGS:          set to execute all combinations of\n"
+          "      REQUIRED_ARGS: arguments always passed to the compiler\n"
+          "      DMD:           compiler to use, ex: ../src/dmd\n"
+          "      OS:            win32, linux, freebsd, osx\n"
+          "      RESULTS_DIR:   base directory for test results\n"
           "   windows vs non-windows portability env vars:\n"
-          "      DSEP:        \\\\ or /\n"
-          "      SEP:         \\ or /\n"
-          "      OBJ:        .obj or .o\n"
-          "      EXE:        .exe or <null>\n");
+          "      DSEP:          \\\\ or /\n"
+          "      SEP:           \\ or /\n"
+          "      OBJ:          .obj or .o\n"
+          "      EXE:          .exe or <null>\n");
 }
 
 enum TestMode