Only use blx if available

Introduce ARM version for the target architecture in order to determine
if blx instruction can be used or not. Availability of blx instruction
allows for more scenarii supported in R_ARM_CALL relocation. It should
also be useful when introducing support for the R_ARM_THM_CALL
relocation.

tcc.h

@@ -105,6 +105,14 @@
 #define TCC_TARGET_I386
 #endif
 
+#if defined (TCC_TARGET_ARM) && !defined(TCC_ARM_VERSION)
+  #ifdef TCC_ARM_HARDFLOAT
+    #define TCC_ARM_VERSION 7
+  #else
+    #define TCC_ARM_VERSION 4
+  #endif
+#endif
+
 #if !defined(TCC_UCLIBC) && !defined(TCC_TARGET_ARM) && \
     !defined(TCC_TARGET_C67) && !defined(TCC_TARGET_X86_64)
 #define CONFIG_TCC_BCHECK /* enable bound checking code */