Always define rd_ut_coverage_check

Define `rd_ut_coverage_check` even in non-devel mode as the `lds-gen.py`
script adds the symbol unconditionally.

Otherwise LLD complains about ld:

```
error: version script assignment of 'global' to symbol 'rd_ut_coverage_check' failed: symbol not defined
```

Fixes #4593

src/rdunittest.c

@@ -104,6 +104,17 @@ rd_ut_coverage_check(const char *file, const char *func, int line, int covnr) {
 }
 /**@}*/
 
+#else
+
+void rd_ut_coverage(const char * /* file */, const char * /* func */, int /* line */, int /* covnr */) {
+}
+
+
+int64_t
+rd_ut_coverage_check(const char * /* file */, const char * /* func */, int /* line */, int /* covnr */) {
+    return 1;
+}
+
 #endif /* ENABLE_CODECOV */
 
 

src/rdunittest.h

@@ -188,6 +188,10 @@ int rd_unittest(void);
  * @{
  */
 
+void rd_ut_coverage(const char *file, const char *func, int line, int covnr);
+int64_t
+rd_ut_coverage_check(const char *file, const char *func, int line, int covnr);
+
 #if ENABLE_CODECOV
 
 /* @define When adding new code coverages, use the next value and increment
@@ -209,10 +213,6 @@ int rd_unittest(void);
         rd_ut_coverage_check(__FILE__, __FUNCTION__, __LINE__, COVNR)
 
 
-void rd_ut_coverage(const char *file, const char *func, int line, int covnr);
-int64_t
-rd_ut_coverage_check(const char *file, const char *func, int line, int covnr);
-
 #else
 
 /* Does nothing if ENABLE_CODECOV is not set */