Teach GDB about more Windows entry points

Windows programs have several conventional entry points depending on
various circumstances. Upstream GDB is only aware of "main" and the
"start" command behaves poorly or incorrectly otherwise.

Dockerfile

@@ -338,7 +338,9 @@ RUN /libiconv-$LIBICONV_VERSION/configure \
  && make install
 
 WORKDIR /gdb
-RUN sed -i 's/quiet = 0/quiet = 1/' /gdb-$GDB_VERSION/gdb/main.c \
+COPY src/gdb-*.patch $PREFIX/src/
+RUN cat $PREFIX/src/gdb-*.patch | patch -d/gdb-$GDB_VERSION -p1 \
+ && sed -i 's/quiet = 0/quiet = 1/' /gdb-$GDB_VERSION/gdb/main.c \
  && /gdb-$GDB_VERSION/configure \
  --host=$ARCH \
  --with-libexpat-prefix=/deps \

src/gdb-000-alternate-main.patch

@@ -0,0 +1,26 @@
+--- a/gdb/symtab.c
++++ b/gdb/symtab.c
+@@ -6300,6 +6300,23 @@
+ if (symbol_found_p)
+ return;
+
++ if (gdbarch_osabi (target_gdbarch ()) == GDB_OSABI_WINDOWS)
++ {
++ static const char *const mains[] = {
++ "wmain", "WinMain", "wWinMain", "WinMainCRTStartup", "mainCRTStartup"
++ };
++ for (const char *main : mains)
++ {
++ struct bound_minimal_symbol msym;
++ msym = lookup_minimal_symbol (main, NULL, NULL);
++ if (msym.minsym != NULL)
++ {
++ set_main_name (main, language_unknown);
++ return;
++ }
++ }
++ }
++
+ set_main_name ("main", language_unknown);
+ }
+