tccrun.c: standalone backtraces with -bt[N] or -b

This makes it possible to get backtraces with executables
(including DLLs/SOs) like we had it already with -g -run.

Option -b includes -bt, and -bt includes -g.

- new file lib/bt-exe.c: used to link rt_printline and the
  exception handler from tccrun.c into executables/DLLs.

- new file lib/bt-log.c: provides a function that may be
  called from user code to print out a backtrace with a
  message (currently for i386/x86_64 only):

     int (*tcc_backtrace)(const char *fmt, ...);

  As an extra hack, if 'fmt' is prefixed like "^file.c^..."
  then the backtrace will skip calls from within 'file.c'.

- new file lib/bt-dll.c:  used on win32 to link the backtrace
  and bcheck functions with the main module at runtime

- bcheck.c: now uses the tcc_backtrace function from above

- tccgen.c: minor cleanups

- tccelf.c: stab sections get SHF_ALLOC for easy access.
  Also in relocate_section(): 64bit relocations for stabs
  in DLLs cannot work.  To find DLL addresses, the DLL base
  is added manually in tccrun.c via rc.prog_base instead.

- tccpe.c: there are some changes to allow merging sections,
  used to merge .finit_array into .data in the first place.

- tccpp.c: tcc -run now #defines __TCC_RUN__
  also: refactor a line in tal_realloc that was incompatible
  with bcheck

- tcctest.c: fixed a problem with r12 which tcc cannot preserve
  as well as gcc does.

- tests2/112_backtrace.c: test the feature and the bcheck test18
  that previously was in boundtest.c

lib/bt-dll.c

@@ -0,0 +1,67 @@
+/* ------------------------------------------------------------- */
+/* stubs for calling bcheck functions from a dll. */
+
+#include <windows.h>
+#include <stdio.h>
+
+#define REDIR_ALL \
+  REDIR(__bt_init) \
+  REDIR(tcc_backtrace) \
+  \
+  REDIR(__bound_ptr_add) \
+  REDIR(__bound_ptr_indir1) \
+  REDIR(__bound_ptr_indir2) \
+  REDIR(__bound_ptr_indir4) \
+  REDIR(__bound_ptr_indir8) \
+  REDIR(__bound_ptr_indir12) \
+  REDIR(__bound_ptr_indir16) \
+  REDIR(__bound_local_new) \
+  REDIR(__bound_local_delete) \
+  REDIR(__bound_new_region) \
+  \
+  REDIR(__bound_free) \
+  REDIR(__bound_malloc) \
+  REDIR(__bound_realloc) \
+  REDIR(__bound_memcpy) \
+  REDIR(__bound_memcmp) \
+  REDIR(__bound_memmove) \
+  REDIR(__bound_memset) \
+  REDIR(__bound_strlen) \
+  REDIR(__bound_strcpy) \
+  REDIR(__bound_strncpy) \
+  REDIR(__bound_strcmp) \
+  REDIR(__bound_strncmp) \
+  REDIR(__bound_strcat) \
+  REDIR(__bound_strchr) \
+  REDIR(__bound_strdup)
+
+#define REDIR(s) void *s;
+static struct { REDIR_ALL } all_ptrs;
+#undef REDIR
+#define REDIR(s) #s"\0"
+static const char all_names[] = REDIR_ALL;
+#undef REDIR
+#define REDIR(s) __asm__(".global "#s";"#s": jmp *%0" : : "m" (all_ptrs.s) );
+static void all_jmps() { REDIR_ALL }
+#undef REDIR
+
+void __bt_init_dll(int bcheck)
+{
+    const char *s = all_names;
+    void **p = (void**)&all_ptrs;
+    do {
+        *p = (void*)GetProcAddress(GetModuleHandle(NULL), (char*)s);
+        if (NULL == *p) {
+            char buf[100];
+            sprintf(buf,
+                "Error: function '%s()' not found in executable. "
+                "(Need -bt or -b for linking the exe.)", s);
+            if (GetStdHandle(STD_ERROR_HANDLE))
+                fprintf(stderr, "TCC/BCHECK: %s\n", buf), fflush(stderr);
+            else
+                MessageBox(NULL, buf, "TCC/BCHECK", MB_ICONERROR);
+            ExitProcess(1);
+        }
+        s = strchr(s,'\0') + 1, ++p;
+    } while (*s && (bcheck || p < &all_ptrs.__bound_ptr_add));
+}