Fix -Wl,-nostdlib behaviour for compatibility with other compilers

TCC treats -nostdlib and -Wl,-nostdlib as equivalent, but on other compilers
which call a discrete linker, -nostdlib behaves as on tcc (not adding
startfiles/libc/endfiles) by modifying the ld command line, but -Wl,-nostdlib
adds -nostdlib to the ld cmdline, which stops the linker searching the default
directories for libraries.

libtcc.c

@@ -924,7 +924,8 @@ LIBTCCAPI int tcc_set_output_type(TCCState *s, int output_type)
         return 0;
     }
 
-    tcc_add_library_path(s, CONFIG_TCC_LIBPATHS);
+    if (!s->nostdlib_paths)
+        tcc_add_library_path(s, CONFIG_TCC_LIBPATHS);
 
 #ifdef TCC_TARGET_PE
 # ifdef TCC_IS_NATIVE
@@ -1383,7 +1384,7 @@ static int tcc_set_linker(TCCState *s, const char *option)
         if (link_option(option, "Bsymbolic", &p)) {
             s->symbolic = 1;
         } else if (link_option(option, "nostdlib", &p)) {
-            s->nostdlib = 1;
+            s->nostdlib_paths = 1;
         } else if (link_option(option, "e=", &p)
                ||  link_option(option, "entry=", &p)) {
             copy_linker_arg(&s->elf_entryname, p, 0);

tcc-doc.texi

@@ -333,9 +333,6 @@ Link your program with dynamic library libxxx.so or static library
 libxxx.a. The library is searched in the paths specified by the
 @option{-L} option and @env{LIBRARY_PATH} variable.
 
-@item -nostdlib
-Don't implicitly link with libc, the C runtime files, and libtcc1.
-
 @item -Bdir
 Set the path where the tcc internal libraries (and include files) can be
 found (default is @file{PREFIX/lib/tcc}).
@@ -357,6 +354,14 @@ opened with @code{dlopen()} needs to access executable symbols.
 @item -r
 Generate an object file combining all input files.
 
+@item -nostdlib
+Don't implicitly link with libc, the C runtime files, and libtcc1.
+
+@item -Wl,-nostdlib
+Don't search the default paths for libraries (@file{/usr/local/lib},
+@file{/usr/lib} and @file{/lib}). Only the paths specified with @option{-L}
+and @env{LIBRARY_PATH} are searched.
+
 @item -Wl,-rpath=path
 Put custom search path for dynamic libraries into executable.
 

tcc.c

@@ -98,6 +98,7 @@ static const char help2[] =
     "  -On                           same as -D__OPTIMIZE__ for n > 0\n"
     "  -Wp,-opt                      same as -opt\n"
     "  -include file                 include 'file' above each input file\n"
+    "  -nostdlib                     do not link with standard crt/libs\n"
     "  -isystem dir                  add 'dir' to system include path\n"
     "  -static                       link to static libraries (not recommended)\n"
     "  -dumpversion                  print version\n"
@@ -132,7 +133,7 @@ static const char help2[] =
     "  no-sse                        disable floats on x86_64\n"
 #endif
     "-Wl,... linker options:\n"
-    "  -nostdlib                     do not link with standard crt/libs\n"
+    "  -nostdlib                     do not search standard library paths\n"
     "  -[no-]whole-archive           load lib(s) fully/only as needed\n"
     "  -export-all-symbols           same as -rdynamic\n"
     "  -export-dynamic               same as -rdynamic\n"

tcc.h

@@ -729,6 +729,7 @@ struct TCCState {
     unsigned char verbose; /* if true, display some information during compilation */
     unsigned char nostdinc; /* if true, no standard headers are added */
     unsigned char nostdlib; /* if true, no standard libraries are added */
+    unsigned char nostdlib_paths; /* if true, the default paths are not searched for libraries */
     unsigned char nocommon; /* if true, do not use common symbols for .bss data */
     unsigned char static_link; /* if true, static linking is performed */
     unsigned char rdynamic; /* if true, all symbols are exported */