[utest][klibc] add rt_sprintf family functions test cases

Author: mysterywolf

Diff for: bsp/stm32/stm32l475-atk-pandora/board/linker_scripts/link.lds

@@ -40,6 +40,12 @@ SECTIONS
         KEEP(*(VSymTab))
         __vsymtab_end = .;
 
+        /* section information for utest */
+        . = ALIGN(4);
+        __rt_utest_tc_tab_start = .;
+        KEEP(*(UtestTcTab))
+        __rt_utest_tc_tab_end = .;
+
         /* section information for initial. */
         . = ALIGN(4);
         __rt_init_start = .;

Diff for: src/klibc/Kconfig

@@ -1,7 +1,7 @@
 menu "klibc options"
     menu "rt_vsnprintf options"
         config RT_KLIBC_USING_LIBC_VSNPRINTF
-            bool "Enable rt_vsnprintf to use libc vsscanf"
+            bool "Enable rt_vsnprintf to use libc vsnprintf"
             default n
 
         config RT_KLIBC_USING_VSNPRINTF_LONGLONG

Diff for: src/klibc/rt_vsnprintf_tiny.c

@@ -448,7 +448,7 @@ int rt_vsnprintf(char *buf, rt_size_t size, const char *fmt, va_list args)
             s = va_arg(args, char *);
             if (!s)
             {
-                s = "(NULL)";
+                s = "(null)";
             }
 
             for (len = 0; (len != field_width) && (s[len] != '\0'); len++);

Diff for: src/klibc/utest/SConscript

@@ -3,7 +3,7 @@ from building import *
 src = []
 
 if GetDepend('RT_USING_CI_ACTION') or GetDepend('RT_UTEST_TC_USING_KLIBC'):
-    src += Glob('tc_*.c')
+    src += Glob('TC_*.c')
 
 group = DefineGroup('utestcases', src, depend = [''])