meson: Allow CUDA_PATH fallback on linux

That's what we've supported via autotools build

Fixes: https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/issues/966

sys/meson.build

@@ -27,38 +27,6 @@ cudart_dep = dependency('', required : false)
 cuda_libdir = ''
 cuda_incdir = ''
 
-if host_machine.system() == 'windows'
-  # On windows, CUDA_PATH env will be set by installer
-  cuda_root = run_command(python3, '-c', 'import os; print(os.environ.get("CUDA_PATH"))').stdout().strip()
-  if cuda_root != '' and cuda_root != 'None'
-    arc = ''
-    if build_machine.cpu_family() == 'x86_64'
-      arc = 'x64'
-    else
-      arc = 'Win32'
-    endif
-    cuda_libdir = join_paths (cuda_root, 'lib', arc)
-    cuda_incdir = join_paths (cuda_root, 'include')
-    cuda_lib = cc.find_library('cuda', dirs: cuda_libdir, required: false)
-    cudart_lib = cc.find_library('cudart', dirs: cuda_libdir, required: false)
-    if cuda_lib.found()
-      cuda_header_found = cc.has_header('cuda.h', args: '-I' + cuda_incdir)
-      cuda_lib_found = cc.has_function('cuInit', dependencies: cuda_lib)
-      if cuda_header_found and cuda_lib_found
-        cuda_dep = declare_dependency(include_directories: include_directories(cuda_incdir),
-                                      dependencies: cuda_lib)
-      endif
-    endif
-
-    if cudart_lib.found()
-      cudart_header_found = cc.has_header('cuda_runtime_api.h', args: '-I' + cuda_incdir)
-      cudart_lib_found = cc.has_function('cudaGetErrorString', dependencies: cudart_lib)
-      if cudart_header_found and cudart_lib_found
-        cudart_dep = declare_dependency(dependencies: cudart_lib)
-      endif
-    endif
-  endif
-else
 cuda_versions = [
     '10.1',
     '10.0',
@@ -100,6 +68,44 @@ else
     cudart_dep = dependency('', required : false)
   endif
 endif
+
+if not cuda_dep.found() or not cudart_dep.found()
+  cuda_root = run_command(python3, '-c', 'import os; print(os.environ.get("CUDA_PATH"))').stdout().strip()
+  if cuda_root != '' and cuda_root != 'None'
+    if host_machine.system() == 'windows'
+      arc = ''
+      if build_machine.cpu_family() == 'x86_64'
+        arc = 'x64'
+      else
+        arc = 'Win32'
+      endif
+      cuda_libdir = join_paths (cuda_root, 'lib', arc)
+    else
+      cuda_libdir = [join_paths (cuda_root, 'lib'), join_paths (cuda_root, 'lib', 'stubs'),
+                     join_paths (cuda_root, 'lib64'), join_paths (cuda_root, 'lib64', 'stubs')]
+    endif
+    cuda_incdir = join_paths (cuda_root, 'include')
+    cuda_lib = cc.find_library('cuda', dirs: cuda_libdir, required: false)
+    cudart_lib = cc.find_library('cudart', dirs: cuda_libdir, required: false)
+
+    if cuda_lib.found()
+      cuda_header_found = cc.has_header('cuda.h', args: '-I' + cuda_incdir)
+      cuda_lib_found = cc.has_function('cuInit', dependencies: cuda_lib)
+      if cuda_header_found and cuda_lib_found
+        cuda_dep = declare_dependency(include_directories: include_directories(cuda_incdir),
+                                      dependencies: cuda_lib)
+      endif
+    endif
+
+    if cudart_lib.found()
+      cudart_header_found = cc.has_header('cuda_runtime_api.h', args: '-I' + cuda_incdir)
+      cudart_lib_found = cc.has_function('cudaGetErrorString', dependencies: cudart_lib)
+      if cudart_header_found and cudart_lib_found
+        cudart_dep = declare_dependency(dependencies: cudart_lib)
+      endif
+    endif
+
+  endif
 endif
 
 if cuda_dep.found() and cudart_dep.found()

sys/nvenc/meson.build

@@ -13,7 +13,7 @@ if nvenc_option.disabled()
   subdir_done()
 endif
 
-if host_machine.system() == 'windows'
+if cuda_dep.type_name() == 'internal'
   if cc.has_header('cuda_gl_interop.h', args: '-I' + cuda_incdir)
     use_nvenc_gl = true
   endif