SDL: cmake: Fix ALSA "Unable to find..." warning

From e3395a75858373ddea040aca2ea210dff2dbead7 Mon Sep 17 00:00:00 2001
From: Robert Edmonds <[EMAIL REDACTED]>
Date: Sat, 6 Apr 2024 12:19:55 -0400
Subject: [PATCH] cmake: Fix ALSA "Unable to find..." warning

If cmake is invoked with -DSDL_ALSA=OFF, the misleading warning
message "Unable to find the alsa development library" is printed.
It's misleading because no attempt was actually made to find the ALSA
development library. It's always printed by the CheckALSA macro if
SDL_ALSA is false.

This commit moves this warning message in the CheckALSA macro to being
printed if ALSA_FOUND is false. However, I don't see an explicit warning
message like this for the other macros that search for development
libraries, so I wonder if the message shouldn't just be removed
entirely. It seems redundant with the "Could NOT find ALSA ..." message
generated by cmake.

Before this commit:

    $ cmake -B build -DSDL_ALSA=OFF
    [...]
    CMake Warning at cmake/sdlchecks.cmake:125 (message):
      Unable to find the alsa development library
    Call Stack (most recent call first):
      CMakeLists.txt:1530 (CheckALSA)
    [...]
    -- Options:
    --   SDL_ALSA                    (Wanted: OFF): OFF
    [...]

    $ cmake -B build -DSDL_ALSA=ON
    [...]
    -- Could NOT find ALSA (missing: ALSA_LIBRARY ALSA_INCLUDE_DIR)
    [...]
    -- Options:
    --   SDL_ALSA                    (Wanted: ON): OFF
    [...]

After this commit:

    $ cmake -B build -DSDL_ALSA=OFF
    [...]
    -- Options:
    --   SDL_ALSA                    (Wanted: OFF): OFF
    [...]

    $ cmake -B build -DSDL_ALSA=ON
    [...]
    -- Could NOT find ALSA (missing: ALSA_LIBRARY ALSA_INCLUDE_DIR)
    CMake Warning at cmake/sdlchecks.cmake:123 (message):
      Unable to find the alsa development library
    Call Stack (most recent call first):
      CMakeLists.txt:1530 (CheckALSA)
    [...]
    -- Options:
    --   SDL_ALSA                    (Wanted: ON): OFF
    [...]

All of the cmake invocations above were without the libasound2-dev
package installed.
---
 cmake/sdlchecks.cmake | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/cmake/sdlchecks.cmake b/cmake/sdlchecks.cmake
index 6a12b3049f0f3..0f1480f1855c3 100644
--- a/cmake/sdlchecks.cmake
+++ b/cmake/sdlchecks.cmake
@@ -119,10 +119,11 @@ macro(CheckALSA)
         sdl_link_dependency(alsa LIBS ALSA::ALSA CMAKE_MODULE ALSA PKG_CONFIG_SPECS "${ALSA_PKG_CONFIG_SPEC}")
       endif()
       set(HAVE_SDL_AUDIO TRUE)
+    else()
+      message(WARNING "Unable to find the alsa development library")
     endif()
   else()
     set(HAVE_ALSA FALSE)
-    message(WARNING "Unable to find the alsa development library")
   endif()
 endmacro()