Make an inline static so we can build with coverage enabled.

src/lib/string/compat_ctype.h

@@ -31,10 +31,10 @@ extern const uint8_t TOR_TOLOWER_TABLE[];
 #define TOR_TOLOWER(c) (TOR_TOLOWER_TABLE[(uint8_t)c])
 #define TOR_TOUPPER(c) (TOR_TOUPPER_TABLE[(uint8_t)c])
 
-inline int hex_decode_digit(char c);
+static inline int hex_decode_digit(char c);
 
 /** Helper: given a hex digit, return its value, or -1 if it isn't hex. */
-inline int
+static inline int
 hex_decode_digit(char c)
 {
   switch (c) {