Support -M, -MM, and -MMD

Add support for some more options to generate dependency fragments.
-M is likes -MD but doesn't compile anything so the command won't fail
when just supplied a file without all the relevant libs.
-MM and -MMD are like their counterparts but skip system libs.

Note the behavior of -MD has changed to include system libs. Use -MMD
for the old behavior. This matches gcc's corresponding flags

libtcc.c

@@ -1502,8 +1502,11 @@ enum {
     TCC_OPTION_w,
     TCC_OPTION_pipe,
     TCC_OPTION_E,
+    TCC_OPTION_M,
     TCC_OPTION_MD,
     TCC_OPTION_MF,
+    TCC_OPTION_MM,
+    TCC_OPTION_MMD,
     TCC_OPTION_x,
     TCC_OPTION_ar,
     TCC_OPTION_impdef,
@@ -1568,8 +1571,11 @@ static const TCCOption tcc_options[] = {
     { "w", TCC_OPTION_w, 0 },
     { "pipe", TCC_OPTION_pipe, 0},
     { "E", TCC_OPTION_E, 0},
+    { "M", TCC_OPTION_M, 0},
     { "MD", TCC_OPTION_MD, 0},
     { "MF", TCC_OPTION_MF, TCC_OPTION_HAS_ARG },
+    { "MM", TCC_OPTION_MM, 0},
+    { "MMD", TCC_OPTION_MMD, 0},
     { "x", TCC_OPTION_x, TCC_OPTION_HAS_ARG },
     { "ar", TCC_OPTION_ar, 0},
 #ifdef TCC_TARGET_PE
@@ -1906,8 +1912,20 @@ reparse:
         case TCC_OPTION_P:
             s->Pflag = atoi(optarg) + 1;
             break;
+        case TCC_OPTION_M:
+            s->include_sys_deps = 1;
+            // fall through
+        case TCC_OPTION_MM:
+            s->just_deps = 1;
+            if(!s->deps_outfile)
+                s->deps_outfile = tcc_strdup("-");
+            // fall through
+        case TCC_OPTION_MMD:
+            s->gen_deps = 1;
+            break;
         case TCC_OPTION_MD:
             s->gen_deps = 1;
+            s->include_sys_deps = 1;
             break;
         case TCC_OPTION_MF:
             s->deps_outfile = tcc_strdup(optarg);

tcc-doc.texi

@@ -370,9 +370,19 @@ to trigger a stack trace with a message on demand.
 Misc options:
 
 @table @option
+
+@item -M
+Just output makefile fragment with dependencies
+
+@item -MM
+Like -M except mention only user header files, not system header files.
+
 @item -MD
 Generate makefile fragment with dependencies.
 
+@item -MMD
+Like -MD except mention only user header files, not system header files.
+
 @item -MF depfile
 Use @file{depfile} as output for -MD.
 

tcc.c

@@ -70,7 +70,10 @@ static const char help[] =
     "  -nostdinc    do not use standard system include paths\n"
     "  -nostdlib    do not link with standard crt and libraries\n"
     "  -Bdir        set tcc's private include/library dir\n"
+    "  -M           just output makefile fragment with dependencies\n"
+    "  -MM          Like -M but ignore system libs\n"
     "  -MD          generate dependency file for make\n"
+    "  -MMD         Like -MMD but ignore system libs\n"
     "  -MF file     specify dependency file name\n"
 #if defined(TCC_TARGET_I386) || defined(TCC_TARGET_X86_64)
     "  -m32/64      defer to i386/x86_64 cross compiler\n"
@@ -250,7 +253,7 @@ static char *default_outputfile(TCCState *s, const char *first_file)
         strcpy(ext, ".exe");
     else
 #endif
-    if (s->output_type == TCC_OUTPUT_OBJ && !s->option_r && *ext)
+    if ((s->just_deps || s->output_type == TCC_OUTPUT_OBJ) && !s->option_r && *ext)
         strcpy(ext, ".o");
     else
         strcpy(buf, "a.out");
@@ -380,7 +383,7 @@ redo:
         } else {
             if (!s->outfile)
                 s->outfile = default_outputfile(s, first_file);
-            if (tcc_output_file(s, s->outfile))
+            if (!s->just_deps && tcc_output_file(s, s->outfile))
                 ret = 1;
             else if (s->gen_deps)
                 gen_makedeps(s, s->outfile, s->deps_outfile);

tcc.h

@@ -975,7 +975,9 @@ struct TCCState {
     char *outfile; /* output filename */
     unsigned char option_r; /* option -r */
     unsigned char do_bench; /* option -bench */
+    int just_deps; /* option -M  */
     int gen_deps; /* option -MD  */
+    int include_sys_deps; /* option -MD  */
     char *deps_outfile; /* option -MF */
     int argc;
     char **argv;

tccpp.c

@@ -1924,7 +1924,7 @@ ST_FUNC void preprocess(int is_bof)
                 while (i == 1 && (bf = bf->prev))
                     i = bf->include_next_index;
                 /* skip system include files */
-                if (n - i > s1->nb_sysinclude_paths)
+                if (s1->include_sys_deps || n - i > s1->nb_sysinclude_paths)
                     dynarray_add(&s1->target_deps, &s1->nb_target_deps,
                         tcc_strdup(buf1));
             }