use the system RtAudio on Linux

cmake/Modules/FindRtAudio.cmake

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+# https://github.com/idiap/juicer/blob/master/cmake/FindRtAudio.cmake
+#
+# Copyright 2015 by Idiap Research Institute
+#
+# Licensed under 3-clause BSD.
+#
+# Author(s):
+#   Phil Garner, November 2015
+#
+# ...but basically copied from FindSndFile in libube, in turn from the examples
+# on the web.
+#
+
+#
+# Try to find RtAudio
+# Once done this will define
+#  RTAUDIO_FOUND          - System has RtAudio
+#  RTAUDIO_INCLUDE_DIR    - The RtAudio include directories
+#  RTAUDIO_LIBRARIES      - The libraries needed to use RtAudio
+#  RTAUDIO_DEFINITIONS    - Compiler switches required for using RtAudio
+#  RTAUDIO_VERSION_STRING - the version of RtAudio found
+#
+
+find_package(PkgConfig)
+pkg_check_modules(PC_RTAUDIO rtaudio)
+
+set(RTAUDIO_DEFINITIONS ${PC_RTAUDIO_CFLAGS_OTHER})
+set(RTAUDIO_VERSION_STRING ${PC_RTAUDIO_VERSION})
+
+find_path(
+  RTAUDIO_INCLUDE_DIR RtAudio.h
+  HINTS ${PC_RTAUDIO_INCLUDEDIR} ${PC_RTAUDIO_INCLUDE_DIRS}
+)
+
+find_library(
+  RTAUDIO_LIBRARIES NAMES rtaudio
+  HINTS ${PC_RTAUDIO_LIBDIR} ${PC_RTAUDIO_LIBRARY_DIRS}
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+  RtAudio
+  REQUIRED_VARS RTAUDIO_LIBRARIES RTAUDIO_INCLUDE_DIR
+  VERSION_VAR RTAUDIO_VERSION_STRING
+)
+
+#mark_as_advanced(RTAUDIO_INCLUDE_DIR RTAUDIO_LIBRARIES)
+