[vdso] use the default arch/abi flags in risc-v vDSO building.

components/lwp/vdso/user/arch/risc-v/SConstruct

@@ -1,5 +1,6 @@
 import os
 import sys
+import subprocess
 
 arguments = sys.argv[2]
 vdso_usr  = arguments
@@ -7,7 +8,32 @@ vdso_path = os.path.join(vdso_usr, '..', '..', '..')
 
 EXEC_PATH = os.getenv('RTT_EXEC_PATH') or '/usr/bin'
 PREFIX    = os.getenv('RTT_CC_PREFIX') or 'riscv64-none-elf-'
-DEVICE    = os.getenv('RTT_DEVICE') or ' -march=rv64imafdc -mabi=lp64'
+
+def get_riscv64_default_arch_abi(gcc_bin):
+    try:
+        result = subprocess.check_output(
+            [gcc_bin, '-Q', '--help=target'],
+            universal_newlines=True
+        )
+        arch = None
+        abi = None
+        for line in result.splitlines():
+            if '-march=' in line and '[default]' in line:
+                arch = line.strip().split()[0]
+            if '-mabi=' in line and '[default]' in line:
+                abi = line.strip().split()[0]
+        return arch, abi
+    except Exception as e:
+        print("Error getting arch/abi:", e)
+        return None, None
+
+# get the gcc path
+CC_BIN = PREFIX + 'gcc'
+arch, abi = get_riscv64_default_arch_abi(CC_BIN)
+if arch and abi:
+    DEVICE = f' {arch} {abi} '
+else:
+    DEVICE = ' -march=rv64imafdc -mabi=lp64'  # fallback
 
 CC      = PREFIX + 'gcc'
 CPP     = PREFIX + 'cpp'