A gcc preprocessor option -dD added

With this option on a defines are included into the output
(inside comments). This will allow to debug a problems like:

    In file included from math.c:8:
    In file included from /usr/include/math.h:43:
    /usr/include/bits/nan.h:52: warning: NAN redefined

1 files changed, 10 insertions, 0 deletions

diff --git a/libtcc.c b/libtcc.c
index 3581ffb..72524eb 100644
--- a/libtcc.c
+++ b/libtcc.c
@@ -1656,6 +1656,7 @@ enum {
     TCC_OPTION_b,
     TCC_OPTION_g,
     TCC_OPTION_c,
+    TCC_OPTION_d,
     TCC_OPTION_float_abi,
     TCC_OPTION_static,
     TCC_OPTION_shared,
@@ -1709,6 +1710,7 @@ static const TCCOption tcc_options[] = {
 #endif
     { "g", TCC_OPTION_g, TCC_OPTION_HAS_ARG | TCC_OPTION_NOSEP },
     { "c", TCC_OPTION_c, 0 },
+    { "d", TCC_OPTION_d, TCC_OPTION_HAS_ARG | TCC_OPTION_NOSEP },
 #ifdef TCC_TARGET_ARM
     { "mfloat-abi", TCC_OPTION_float_abi, TCC_OPTION_HAS_ARG },
 #endif
@@ -1848,6 +1850,14 @@ PUB_FUNC int tcc_parse_args(TCCState *s, int argc, char **argv)
                 tcc_warning("-c: some compiler action already specified (%d)", s->output_type);
             s->output_type = TCC_OUTPUT_OBJ;
             break;
+        case TCC_OPTION_d:
+    	    if (*optarg != 'D') {
+    		if (s->warn_unsupported)
+            	    goto unsupported_option;
+                 tcc_error("invalid option -- '%s'", r);
+    	    }
+            s->dflag = 1;
+            break;
 #ifdef TCC_TARGET_ARM
         case TCC_OPTION_float_abi:
             /* tcc doesn't support soft float yet */