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 <[email protected]>

Author: Chris Friedt

lib/libc/minimal/include/ctype.h

@@ -26,6 +26,11 @@ static inline int isalpha(int c)
 	return (('a' <= c) && (c <= 'z'));
 }
 
+static inline int isblank(int c)
+{
+	return ((c == ' ') || (c == '\t'));
+}
+
 static inline int isspace(int c)
 {
 	return ((c == ' ') || (('\t' <= c) && (c <= '\r')));
@@ -46,6 +51,11 @@ static inline int isdigit(int a)
 	return (('0' <= a) && (a <= '9'));
 }
 
+static inline int islower(int c)
+{
+	return (('a' <= c) && (c <= 'z'));
+}
+
 static inline int isxdigit(int a)
 {
 	if (isdigit(a) != 0) {
@@ -73,6 +83,11 @@ static inline int isalnum(int chr)
 	return (isalpha(chr) || isdigit(chr));
 }
 
+static inline int ispunct(int c)
+{
+	return (isgraph(c) && !isalnum(c));
+}
+
 static inline int iscntrl(int c)
 {
 	return ((((unsigned int)c) <= 31U) || (((unsigned int)c) == 127U));