Simple-minded fix for bug #50847

bug #50847: #line directive corrupts #include search path
Keep a second copy of the filename, that isn't changed by the #line directive,
and use that on the initial search path for #include files.

libtcc.c

@@ -581,6 +581,7 @@ ST_FUNC void tcc_open_bf(TCCState *s1, const char *filename, int initlen)
     bf->buf_end = bf->buffer + initlen;
     bf->buf_end[0] = CH_EOB; /* put eob symbol */
     pstrcpy(bf->filename, sizeof(bf->filename), filename);
+    pstrcpy(bf->filename2, sizeof(bf->filename2), filename);
 #ifdef _WIN32
     normalize_slashes(bf->filename);
 #endif

tcc.h

@@ -546,6 +546,7 @@ typedef struct BufferedFile {
     int *ifdef_stack_ptr; /* ifdef_stack value at the start of the file */
     int include_next_index; /* next search path */
     char filename[1024];    /* filename */
+    char filename2[1024];    /* filename not modified by # line directive */
     unsigned char unget[4];
     unsigned char buffer[1]; /* extra size for CH_EOB char */
 } BufferedFile;

tccpp.c

@@ -1792,7 +1792,8 @@ ST_FUNC void preprocess(int is_bof)
                 /* search in file's dir if "header.h" */
                 if (c != '\"')
                     continue;
-                path = file->filename;
+                /* https://savannah.nongnu.org/bugs/index.php?50847 */
+                path = file->filename2;
                 pstrncpy(buf1, path, tcc_basename(path) - path);
 
             } else {