cmake: Fix find_program usage for 3.15

yuzu requires CMake 3.15 yet find_program was using REQUIRED, which is
only available on 3.18 and later. Instead, we check for
"<VAR>-NOTFOUND".

In addition, check for additional requirements before building libusb or
FFmpeg with autotools. Otherwise, CMake configuration will pass yet
compilation will fail.

1 files changed, 9 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 97afaf1a9..f0e892a97 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -473,7 +473,15 @@ if (YUZU_USE_BUNDLED_FFMPEG)
 
         # FFmpeg has source that requires one of nasm or yasm to assemble it.
         # REQUIRED throws an error if not found here during configuration rather than during compilation.
-        find_program(ASSEMBLER NAMES nasm yasm REQUIRED)
+        find_program(ASSEMBLER NAMES nasm yasm)
+        if ("${ASSEMBLER}" STREQUAL "ASSEMBLER-NOTFOUND")
+            message(FATAL_ERROR "One of either `nasm` or `yasm` not found but is required.")
+        endif()
+
+        find_program(AUTOCONF autoconf)
+        if ("${AUTOCONF}" STREQUAL "AUTOCONF-NOTFOUND")
+            message(FATAL_ERROR "Required program `autoconf` not found.")
+        endif()
 
         set(FFmpeg_PREFIX ${PROJECT_SOURCE_DIR}/externals/ffmpeg)
         set(FFmpeg_BUILD_DIR ${PROJECT_BINARY_DIR}/externals/ffmpeg)