[libc] Bring libc in-tree

Moving libc from its separate repo into this one, minor resulting build
fixes, and a hacky way to add -I for libc headers in builds.

src/libraries/libc/j6libc/load_lc_time.c

@@ -0,0 +1,79 @@
+/* _PDCLIB_load_lc_time( const char *, const char * )
+
+   This file is part of the Public Domain C Library (PDCLib).
+   Permission is granted to use, modify, and / or redistribute at will.
+*/
+
+#include <locale.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "j6libc/int.h"
+
+struct _PDCLIB_lc_time_t * _PDCLIB_load_lc_time( const char * path, const char * locale )
+{
+    struct _PDCLIB_lc_time_t * rc = NULL;
+    const char * extension = "_time.dat";
+    char * file = malloc( strlen( path ) + strlen( locale ) + strlen( extension ) + 1 );
+
+    if ( file )
+    {
+        FILE * fh;
+
+        strcpy( file, path );
+        strcat( file, locale );
+        strcat( file, extension );
+
+        if ( ( fh = fopen( file, "rb" ) ) != NULL )
+        {
+            if ( ( rc = malloc( sizeof( struct _PDCLIB_lc_time_t ) ) ) != NULL )
+            {
+                char * data = _PDCLIB_load_lines( fh, 44 );
+
+                if ( data != NULL )
+                {
+                    size_t i;
+
+                    for ( i = 0; i < 12; ++i )
+                    {
+                        rc->month_name_abbr[ i ] = data;
+                        data += strlen( data ) + 1;
+                    }
+
+                    for ( i = 0; i < 12; ++i )
+                    {
+                        rc->month_name_full[ i ] = data;
+                        data += strlen( data ) + 1;
+                    }
+
+                    for ( i = 0; i < 7; ++i )
+                    {
+                        rc->day_name_abbr[ i ] = data;
+                        data += strlen( data ) + 1;
+                    }
+
+                    for ( i = 0; i < 7; ++i )
+                    {
+                        rc->day_name_full[ i ] = data;
+                        data += strlen( data ) + 1;
+                    }
+
+                    rc->alloced = 1;
+                }
+                else
+                {
+                    free( rc );
+                    rc = NULL;
+                }
+            }
+
+            fclose( fh );
+        }
+
+        free( file );
+    }
+
+    return rc;
+}