Update CMakeLists.txt (#784)

* Update CMakeLists.txt

fixes obs builds

src/CMakeLists.txt

@@ -17,13 +17,17 @@ else()
 endif()
 
 if (LINUX)
-    file(STRINGS "/etc/os-release" OS_RELEASE_CONTENTS)
-    foreach(LINE ${OS_RELEASE_CONTENTS})
-        if(LINE MATCHES "^ID=")
-            string(REGEX REPLACE "^ID=\"?\([a-zA-Z]+\)\"?" "\\1" OS_ID ${LINE})
-        endif()
-    endforeach()
-    message(STATUS "Detected Linux distribution: ${OS_ID}")
+    if(EXISTS "/etc/os-release") #  AND IS_READABLE "/etc/os-release" (3.29 cmake required :-( )
+      file(STRINGS "/etc/os-release" OS_RELEASE_CONTENTS)
+      foreach(LINE ${OS_RELEASE_CONTENTS})
+          if(LINE MATCHES "^ID=")
+              string(REGEX REPLACE "^ID=\"?\([a-zA-Z]+\)\"?" "\\1" OS_ID ${LINE})
+          endif()
+      endforeach()
+      message(STATUS "Detected Linux distribution: ${OS_ID}")
+    else()
+      message(STATUS "Unable to read /etc/os-release")
+    endif()
 endif()
 
 if(NOT DEFINED NO_ASAN)