sdl2-std, sdl2-std32: complete link flags

The previous LDFLAGS only provided -lSDL2 -lSDL2main which forced
consumers to chase the missing transitive deps (X11, pthread, dl, rt, m)
in their own Makefiles. Add the full set that sdl2-config --libs
returns so a single include of sdl2-std.mk or sdl2-std32.mk is enough
to link a SDL2 host (32 or 64 bit) program on this target.

Also mark libdreamroq as DONE in FUTURE_IDEAS.md: it is now shipped
inside the sh4zam package and no longer needs a separate clone.

Author: Shockblast

docs/FUTURE_IDEAS.md

@@ -8,7 +8,7 @@ This document contains a list of tools and libraries that were previously in the
   * ~~Description: A small library for the Dreamcast AICA sound subsystem.~~
   * ~~URL: [https://github.com/pcercuei/AICAOS.git](https://github.com/pcercuei/AICAOS.git)~~
 
-- **libdreamroq**
+- **libdreamroq** (DONE)
   * Description: Library for playing RoQ videos.
   * URL: [https://github.com/dreamcastdevs/libdreamroq.git](https://github.com/dreamcastdevs/libdreamroq.git)
 

scripts/registry/mk/sdl2-std.mk

@@ -1,5 +1,8 @@
 # sdl2-std.mk - SDL2 apt (host-64)
 # Source: apt libsdl2-dev:amd64 (multi-arch /usr/lib/x86_64-linux-gnu)
+# Provides the full link set returned by sdl2-config on this target.
 
 SDL2_STD_CFLAGS  := -I/usr/include/SDL2 -D_REENTRANT
-SDL2_STD_LDFLAGS := -L/usr/lib/x86_64-linux-gnu -lSDL2 -lSDL2main
+SDL2_STD_LDFLAGS := -L/usr/lib/x86_64-linux-gnu \
+                     -lSDL2 -lSDL2main \
+                     -lX11 -lpthread -ldl -lrt -lm

scripts/registry/mk/sdl2-std32.mk

@@ -1,5 +1,8 @@
 # sdl2-std32.mk - SDL2 apt (host-32)
 # Source: apt libsdl2-dev:i386 (multi-arch /usr/lib/i386-linux-gnu)
+# Provides the full link set returned by sdl2-config on this target.
 
 SDL2_STD32_CFLAGS  := -I/usr/include/SDL2 -D_REENTRANT
-SDL2_STD32_LDFLAGS := -L/usr/lib/i386-linux-gnu -lSDL2 -lSDL2main
+SDL2_STD32_LDFLAGS := -L/usr/lib/i386-linux-gnu \
+                       -lSDL2 -lSDL2main \
+                       -lX11 -lpthread -ldl -lrt -lm