libandroid-posix-semaphore: pass PREFIX as compiler flag

packages/libandroid-posix-semaphore/build.sh

@@ -7,7 +7,8 @@ TERMUX_PKG_SKIP_SRC_EXTRACT=true
 TERMUX_PKG_BUILD_IN_SRC=true
 
 termux_step_make() {
-	$CC $CFLAGS $CPPFLAGS -I$TERMUX_PKG_BUILDER_DIR -c $TERMUX_PKG_BUILDER_DIR/semaphore.c
+	$CC $CFLAGS $CPPFLAGS -DPREFIX="\"$TERMUX_PREFIX\"" \
+		-c $TERMUX_PKG_BUILDER_DIR/semaphore.c
 	$CC $LDFLAGS -shared semaphore.o -o libandroid-posix-semaphore.so
 	$AR rcu libandroid-posix-semaphore.a semaphore.o
 	cp -f $TERMUX_PKG_BUILDER_DIR/LICENSE $TERMUX_PKG_SRCDIR/

packages/libandroid-posix-semaphore/semaphore.c

@@ -43,6 +43,10 @@
 #define SEM_NSEMS_MAX 256
 #endif // !SEM_NSEMS_MAX
 
+#ifndef PREFIX
+#define PREFIX "/data/data/com.termux/files/usr"
+#endif
+
 static __inline__ char *__strchrnul(const char *s, int c)
 {
     c = (unsigned char)c;
@@ -78,7 +82,7 @@ static char *__sem_mapname(const char *name, char *buf)
         errno = ENAMETOOLONG;
         return 0;
     }
-    memcpy(buf, "/data/data/com.termux/files/usr/tmp/sem.", 40);
+    memcpy(buf, PREFIX"/tmp/sem.", 40);
     memcpy(buf+40, name, p-name+1);
     return buf;
 }