global.h: move __STRING() macro outside !PIC ifdef block

It solves the musl libc compilation issue.

control.c: In function 'snd_ctl_open_conf':
../../include/global.h:98:36: warning: implicit declaration of function '__STRING' [-Wimplicit-function-declaratio]
   98 | #define SND_DLSYM_VERSION(version) __STRING(version)
      |                                    ^~~~~~~~

Fixes: #350
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/global.h

@@ -51,6 +51,11 @@ const char *snd_asoundlib_version(void);
 #define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
 #endif
 
+#ifndef __STRING
+/** \brief Return 'x' argument as string */
+#define __STRING(x)     #x
+#endif
+
 #ifdef PIC /* dynamic build */
 
 /** \hideinitializer \brief Helper macro for #SND_DLSYM_BUILD_VERSION. */
@@ -71,11 +76,6 @@ struct snd_dlsym_link {
 
 extern struct snd_dlsym_link *snd_dlsym_start;
 
-#ifndef __STRING
-/** \brief Return 'x' argument as string */
-#define __STRING(x)     #x
-#endif
-
 /** \hideinitializer \brief Helper macro for #SND_DLSYM_BUILD_VERSION. */
 #define __SND_DLSYM_VERSION(prefix, name, version) _ ## prefix ## name ## version
 /**