libc: minimal: add missing ctype.h functions

Add the functions below to the minimal libc ctype.h since they are
missing, and are required as of C89 (C99 for `isblank()`)

* `isblank()`
* `islower()`
* `ispunct()`

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>

Author: cfriedt

lib/libc/minimal/include/ctype.h

@@ -23,6 +23,11 @@ static inline int isalpha(int c)
 	return (int)((((unsigned)c|32u)-(unsigned)'a') < 26U);
 }
 
+static inline int isblank(int c)
+{
+	return (int)((c == (int)' ') || (c == (int)'\t'));
+}
+
 static inline int isspace(int c)
 {
 	return (int)(c == (int)' ' || ((unsigned)c-(unsigned)'\t') < 5U);
@@ -40,11 +45,21 @@ static inline int isprint(int c)
 			(((unsigned)c) <= (unsigned)'~'));
 }
 
+static inline int ispunct(int c)
+{
+	return (int)(isgraph(c) && !isalnum(c));
+}
+
 static inline int isdigit(int a)
 {
 	return (int)(((unsigned)(a)-(unsigned)'0') < 10U);
 }
 
+static inline int islower(int c)
+{
+	return (int)(((unsigned)(c) - (unsigned)'a') < 26U);
+}
+
 static inline int isxdigit(int a)
 {
 	unsigned int ua = (unsigned int)a;