Makefile.ctr: detect the installed libctru generation

USE_CTRULIB_2 now defaults by probing the toolchain's gspgpu.h for
gspPresentBuffer, so plain make builds correctly against both current
libctru and the legacy ctr toolchain with no flag on the make line.
An explicit USE_CTRULIB_2=0/1 still overrides the probe, and a preset
CTRULIB is honored. The salamander makefile gains the same probe, so
the two makefiles agree on any given install.

Makefile.ctr

@@ -10,7 +10,7 @@ BUILD_3DSX              = 1
 BUILD_3DS               = 0
 BUILD_CIA               = 1
 LIBCTRU_NO_DEPRECATION  = 1
-USE_CTRULIB_2          ?= 0
+USE_CTRULIB_2 ?= $(if $(shell grep -sl gspPresentBuffer $(or $(CTRULIB),$(DEVKITPRO)/libctru)/include/3ds/services/gspgpu.h),1,0)
 LOAD_WITHOUT_CORE_INFO ?= 0
 
 APP_TITLE            = RetroArch 3DS

Makefile.ctr.salamander

@@ -6,7 +6,7 @@ CONSOLE_LOG             = 0
 BUILD_3DSX              = 1
 BUILD_3DS               = 0
 BUILD_CIA               = 1
-USE_CTRULIB_2          ?= 0
+USE_CTRULIB_2 ?= $(if $(shell grep -sl gspPresentBuffer $(or $(CTRULIB),$(DEVKITPRO)/libctru)/include/3ds/services/gspgpu.h),1,0)
 
 APP_TITLE            = RetroArch 3DS
 APP_DESCRIPTION      = RetroArch 3DS