[fusl] Remove code for unsupported architectures

fusl/arch/arm/pthread_arch.h

-#if ((__ARM_ARCH_6K__ || __ARM_ARCH_6ZK__) && !__thumb__) || \
-    __ARM_ARCH_7A__ || __ARM_ARCH_7R__ || __ARM_ARCH >= 7
-
-static inline pthread_t __pthread_self() {
-  char* p;
-  __asm__ __volatile__("mrc p15,0,%0,c13,c0,3" : "=r"(p));
-  return (void*)(p + 8 - sizeof(struct pthread));
-}
-
-#else
-
-static inline pthread_t __pthread_self() {
-#ifdef __clang__
-  char* p;
-  __asm__ __volatile__("bl __a_gettp\n\tmov %0,r0"
-                       : "=r"(p)
-                       :
-                       : "cc", "r0", "lr");
-#else
-  register char* p __asm__("r0");
-  __asm__ __volatile__("bl __a_gettp" : "=r"(p) : : "cc", "lr");
-#endif
-  return (void*)(p + 8 - sizeof(struct pthread));
-}
-
-#endif
-
-#define TLS_ABOVE_TP
-#define TP_ADJ(p) ((char*)(p) + sizeof(struct pthread) - 8)
-
-#define MC_PC arm_pc