fix symbol visibility for automake builds

src/Makefile.am

@@ -3,7 +3,7 @@
 LIBVERSION=0:0:0
 
 INCLUDES = $(all_includes) -I$(top_srcdir)/include
-AM_CFLAGS = -fPIC -Wall
+AM_CFLAGS = ${CFLAGS} -fPIC ${SYMBOL_VISIBILITY}
 
 lib_LTLIBRARIES = librtlsdr.la
 

src/librtlsdr.c

@@ -824,7 +824,7 @@ int rtlsdr_set_testmode(rtlsdr_dev_t *dev, int on)
 	return 0;
 }
 
-rtlsdr_dongle_t *find_known_device(uint16_t vid, uint16_t pid)
+static rtlsdr_dongle_t *find_known_device(uint16_t vid, uint16_t pid)
 {
 	unsigned int i;
 	rtlsdr_dongle_t *device = NULL;