basic,shared: mark eligible functions with _pure_/_const_

Following the recent witch hunt done to static inline functions
I figure we should at least give the compiler some more hint
on optimizations.

src/basic/utf8.h

@@ -6,7 +6,7 @@
 #define UTF8_REPLACEMENT_CHARACTER "\xef\xbf\xbd"
 #define UTF8_BYTE_ORDER_MARK "\xef\xbb\xbf"
 
-bool unichar_is_valid(char32_t c);
+bool unichar_is_valid(char32_t c) _const_;
 
 char* utf8_is_valid_n(const char *str, size_t len_bytes) _pure_;
 static inline char* utf8_is_valid(const char *str) {
@@ -35,10 +35,10 @@ size_t utf16_encode_unichar(char16_t *out, char32_t c);
 char* utf16_to_utf8(const char16_t *s, size_t length /* bytes! */);
 char16_t *utf8_to_utf16(const char *s, size_t length);
 
-size_t char16_strlen(const char16_t *s); /* returns the number of 16-bit words in the string (not bytes!) */
-size_t char16_strsize(const char16_t *s);
+size_t char16_strlen(const char16_t *s) _pure_; /* returns the number of 16-bit words in the string (not bytes!) */
+size_t char16_strsize(const char16_t *s) _pure_;
 
-int utf8_encoded_valid_unichar(const char *str, size_t length);
+int utf8_encoded_valid_unichar(const char *str, size_t length) _pure_;
 int utf8_encoded_to_unichar(const char *str, char32_t *ret_unichar);
 
 static inline bool utf16_is_surrogate(char16_t c) {
@@ -53,8 +53,8 @@ static inline char32_t utf16_surrogate_pair_to_unichar(char16_t lead, char16_t t
         return ((((char32_t) lead - 0xd800U) << 10) + ((char32_t) trail - 0xdc00U) + 0x10000U);
 }
 
-size_t utf8_n_codepoints(const char *str);
-int utf8_char_console_width(const char *str);
-size_t utf8_console_width(const char *str);
+size_t utf8_n_codepoints(const char *str) _pure_;
+int utf8_char_console_width(const char *str) _pure_;
+size_t utf8_console_width(const char *str) _pure_;
 
-size_t utf8_last_length(const char *s, size_t n);
+size_t utf8_last_length(const char *s, size_t n) _pure_;