cuda: check for cuda.h when enabled

Fixes make checkheaders on systems without the Cuda Toolkit, which
was broken after the dynlink changes.
Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -1809,6 +1809,7 @@ HEADERS_LIST="
     asm_types_h
     cdio_paranoia_h
     cdio_paranoia_paranoia_h
+    cuda_h
     dispatch_dispatch_h
     dev_bktr_ioctl_bt848_h
     dev_bktr_ioctl_meteor_h
@@ -5657,6 +5658,7 @@ done
 enabled avfoundation_indev && { check_header_objcc AVFoundation/AVFoundation.h || disable avfoundation_indev; }
 enabled avfoundation_indev && { check_lib2 CoreGraphics/CoreGraphics.h CGGetActiveDisplayList -framework CoreGraphics ||
                                 check_lib2 ApplicationServices/ApplicationServices.h CGGetActiveDisplayList -framework ApplicationServices; }
+enabled cuda              && check_header cuda.h # this is not a dependency
 enabled cuvid             && { enabled cuda ||
                                die "ERROR: CUVID requires CUDA"; }
 enabled chromaprint       && require chromaprint chromaprint.h chromaprint_get_version -lchromaprint

libavutil/Makefile

@@ -166,7 +166,8 @@ OBJS += $(COMPAT_OBJS:%=../compat/%)
 # Windows resource file
 SLIBOBJS-$(HAVE_GNU_WINDRES)            += avutilres.o
 
-SKIPHEADERS-$(CONFIG_CUDA)             += hwcontext_cuda.h
+SKIPHEADERS-$(HAVE_CUDA_H)             += hwcontext_cuda.h
+SKIPHEADERS-$(CONFIG_CUDA)             += hwcontext_cuda_internal.h
 SKIPHEADERS-$(CONFIG_DXVA2)            += hwcontext_dxva2.h
 SKIPHEADERS-$(CONFIG_QSV)           += hwcontext_qsv.h
 SKIPHEADERS-$(CONFIG_VAAPI)            += hwcontext_vaapi.h