Main: split libc into separate source files

Makefile.am

@@ -70,7 +70,10 @@ if WITH_FRAMEBUFFER
 libkernaux_a_SOURCES += src/framebuffer.c
 endif
 if WITH_LIBC
-libkernaux_a_SOURCES += libc/src/main.c
+libkernaux_a_SOURCES += \
+	libc/src/ctype.c \
+	libc/src/stdlib.c \
+	libc/src/string.c
 endif
 if WITH_MBR
 libkernaux_a_SOURCES += src/mbr.c

libc/src/ctype.c

@@ -0,0 +1,15 @@
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <ctype.h>
+
+int isdigit(const int c)
+{
+    return (unsigned)c - '0' < 10;
+}
+
+int isspace(const int c)
+{
+    return c == ' ' || (unsigned)c - '\t' < 5;
+}

libc/src/stdlib.c

@@ -0,0 +1,20 @@
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+int atoi(const char *str)
+{
+    while (isspace(*str)) ++str;
+    bool is_negative = false;
+    switch (*str) {
+    case '-': is_negative = true; // fall through
+    case '+': ++str;
+    }
+    int result = 0;
+    while (isdigit(*str)) result = 10 * result - (*str++ - '0');
+    return is_negative ? result : -result;
+}

libc/src/string.c

@@ -2,34 +2,9 @@
 #include "config.h"
 #endif
 
-#include <ctype.h>
+#include <stddef.h>
-#include <stdbool.h>
-#include <stdlib.h>
 #include <string.h>
 
-int atoi(const char *str)
-{
-    while (isspace(*str)) ++str;
-    bool is_negative = false;
-    switch (*str) {
-    case '-': is_negative = true; // fall through
-    case '+': ++str;
-    }
-    int result = 0;
-    while (isdigit(*str)) result = 10 * result - (*str++ - '0');
-    return is_negative ? result : -result;
-}
-
-int isdigit(const int c)
-{
-    return (unsigned)c - '0' < 10;
-}
-
-int isspace(const int c)
-{
-    return c == ' ' || (unsigned)c - '\t' < 5;
-}
-
 int memcmp(const void *s1, const void *s2, size_t n)
 {
     for (const unsigned char *p1 = s1, *p2 = s2; n--; ++p1, ++p2) {