[bsp] Switch qemu-vexpress-a9 sample to picolibc

This adds the necessary changes to the linker script and
then selects picolibc instead of the default (newlib).

Before:
   text	   data	    bss	    dec	    hex	filename
 561638	   2100	  84928	 648666	  9e5da	rtthread.elf

After:
   text	   data	    bss	    dec	    hex	filename
 525009	    692	  86844	 612545	  958c1	rtthread.elf

Signed-off-by: Keith Packard <keithp@keithp.com>

bsp/qemu-vexpress-a9/.config

@@ -30,9 +30,12 @@ CONFIG_RT_TIMER_THREAD_STACK_SIZE=1024
 #
 # kservice optimization
 #
-# CONFIG_RT_KSERVICE_USING_STDLIB is not set
+CONFIG_RT_KSERVICE_USING_STDLIB=y
+CONFIG_RT_KSERVICE_USING_STDLIB_MEMCPY=y
+CONFIG_RT_KSERVICE_USING_STDLIB_MEMSET=y
 # CONFIG_RT_KSERVICE_USING_TINY_SIZE is not set
 # CONFIG_RT_USING_TINY_FFS is not set
+CONFIG_RT_KSERVICE_USING_PRINTF=y
 # CONFIG_RT_PRINTF_LONGLONG is not set
 CONFIG_RT_DEBUG=y
 CONFIG_RT_DEBUG_COLOR=y

bsp/qemu-vexpress-a9/link.lds

@@ -72,6 +72,23 @@ SECTIONS
         PROVIDE(__dtors_end__ = .);
     }
 
+    . = ALIGN(8);
+    .tdata : {
+	*(.tdata)
+	*(.tdata.*)
+	*(.gnu.linkonce.td.*)
+    }
+
+    .tbss (NOLOAD) : {
+	*(.tbss .tbss.* .gnu.linkonce.tb.*)
+	*(.tcommon)
+    }
+
+    __tdata_source = ADDR(.tdata);
+    __tdata_size = SIZEOF(.tdata);
+    __tbss_size = SIZEOF(.tbss);
+    __tls_size = SIZEOF(.tdata) + SIZEOF(.tbss);
+
     . = ALIGN(8);
     __data_start = .;
     .data :

bsp/qemu-vexpress-a9/rtconfig.h

@@ -26,6 +26,10 @@
 
 /* kservice optimization */
 
+#define RT_KSERVICE_USING_STDLIB
+#define RT_KSERVICE_USING_STDLIB_MEMCPY
+#define RT_KSERVICE_USING_STDLIB_MEMSET
+#define RT_KSERVICE_USING_PRINTF
 #define RT_DEBUG
 #define RT_DEBUG_COLOR
 

bsp/qemu-vexpress-a9/rtconfig.py

@@ -35,6 +35,7 @@ def get_mac_address():
 
 # only support GNU GCC compiler.
 PLATFORM    = 'gcc'
+LIBC        = 'picolibc'
 EXEC_PATH   = r'/usr/bin'
 
 if os.getenv('RTT_EXEC_PATH'):