devel/sdl2: prevent from using linux/input.h if present

OK for this?

Index: Makefile
===================================================================
RCS file: /cvs/ports/devel/sdl2/Makefile,v
diff -u -p -r1.52 Makefile
--- Makefile 13 Oct 2023 22:38:11 -0000 1.52
+++ Makefile 1 Nov 2023 19:08:26 -0000
@@ -5,6 +5,7 @@ DISTNAME= SDL2-${V}
PKGNAME= sdl2-${V}
CATEGORIES= devel
SITES= https://www.libsdl.org/release/
+REVISION= 0

SHARED_LIBS= SDL2 0.14 # 2.28.1

@@ -47,6 +48,8 @@ CONFIGURE_ARGS+= --disable-alsa \
--disable-x11-shared
CONFIGURE_ENV+= CPPFLAGS="-I${LOCALBASE}/include" \
LDFLAGS="-L${LOCALBASE}/lib"
+
+CONFIGURE_ENV += ac_cv_header_linux_input_h=no

.if ${MACHINE_ARCH} == "hppa"
CONFIGURE_ARGS+= --disable-atomic