i386: Remove build support for GCC older than GCC 6

Since GCC 6.2 or later is required to build glibc, remove build support
for GCC older than GCC 6.

Testd with GCC 6.4 and GCC 9.3.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/i386/sysdep.h

@@ -18,8 +18,6 @@
 
 #include <sysdeps/x86/sysdep.h>
 
-#include <features.h> /* For __GNUC_PREREQ.  */
-
 /* It is desirable that the names of PIC thunks match those used by
    GCC so that multiple copies are eliminated by the linker.  Because
    GCC 4.6 and earlier use __i686 in the names, it is necessary to

sysdeps/i386/tls-macros.h

@@ -1,5 +1,3 @@
-#include <features.h> /* For __GNUC_PREREQ.  */
-
 #define TLS_LE(x) \
   ({ int *__l;								      \
      asm ("movl %%gs:0,%0\n\t"						      \
@@ -7,14 +5,6 @@
 	  : "=r" (__l));						      \
      __l; })
 
-#if defined PIC && !__GNUC_PREREQ (5,0)
-# define TLS_IE(x) \
-  ({ int *__l;								      \
-     asm ("movl %%gs:0,%0\n\t"						      \
-	  "subl " #x "@gottpoff(%%ebx),%0"				      \
-	  : "=r" (__l));						      \
-     __l; })
-#else
 #define TLS_IE(x) \
   ({ int *__l, __b;							      \
      asm ("call 1f\n\t"							      \
@@ -27,17 +17,7 @@
 	  "subl " #x "@gottpoff(%%ebx),%0"				      \
 	  : "=r" (__l), "=&b" (__b));					      \
      __l; })
-#endif
 
-#if defined PIC && !__GNUC_PREREQ (5,0)
-# define TLS_LD(x) \
-  ({ int *__l, __c, __d;						      \
-     asm ("leal " #x "@tlsldm(%%ebx),%%eax\n\t"				      \
-	  "call ___tls_get_addr@plt\n\t"				      \
-	  "leal " #x "@dtpoff(%%eax), %%eax"				      \
-	  : "=a" (__l), "=&c" (__c), "=&d" (__d));			      \
-     __l; })
-#else
 #define TLS_LD(x) \
   ({ int *__l, __b, __c, __d;						      \
      asm ("call 1f\n\t"							      \
@@ -51,17 +31,7 @@
 	  "leal " #x "@dtpoff(%%eax), %%eax"				      \
 	  : "=a" (__l), "=&b" (__b), "=&c" (__c), "=&d" (__d));		      \
      __l; })
-#endif
 
-#if defined PIC && !__GNUC_PREREQ (5,0)
-# define TLS_GD(x) \
-  ({ int *__l, __c, __d;						      \
-     asm ("leal " #x "@tlsgd(%%ebx),%%eax\n\t"				      \
-	  "call ___tls_get_addr@plt\n\t"				      \
-	  "nop"								      \
-	  : "=a" (__l), "=&c" (__c), "=&d" (__d));			      \
-     __l; })
-#else
 #define TLS_GD(x) \
   ({ int *__l, __b, __c, __d;						      \
      asm ("call 1f\n\t"							      \
@@ -75,4 +45,3 @@
 	  "nop"								      \
 	  : "=a" (__l), "=&b" (__b), "=&c" (__c), "=&d" (__d));		      \
      __l; })
-#endif

sysdeps/unix/sysv/linux/i386/sysdep.h

@@ -48,7 +48,7 @@
    to compile glibc.  Disable GCC 5 optimization when compiling for
    profiling or when -fno-omit-frame-pointer is used since asm ("ebp")
    can't be used to put the 6th argument in %ebp for syscall.  */
-#if __GNUC_PREREQ (5,0) && !defined PROF && CAN_USE_REGISTER_ASM_EBP
+#if !defined PROF && CAN_USE_REGISTER_ASM_EBP
 # define OPTIMIZE_FOR_GCC_5
 #endif
 
@@ -580,21 +580,6 @@ struct libc_do_syscall_args
 # define EXTRAVAR_5
 #endif
 
-/* Consistency check for position-independent code.  Disabled for GCC 5
-   and above since there is no fixed PIC register in GCC 5 and above.  */
-#if defined __PIC__ && !__GNUC_PREREQ (5,0)
-# define check_consistency()						      \
-  ({ int __res;								      \
-     __asm__ __volatile__						      \
-       (LOAD_PIC_REG_STR (cx) ";"					      \
-	"subl %%ebx, %%ecx;"						      \
-	"je 1f;"							      \
-	"ud2;"								      \
-	"1:\n"								      \
-	: "=c" (__res));						      \
-     __res; })
-#endif
-
 #endif	/* __ASSEMBLER__ */