build: remove fdelt_chk backwards compatibility code

Now that we require glibc 2.17 or later, we no longer need to check for
different return types in fdelt_chk. It was changed from unsigned long
int to long int in glibc 2.16 . See this commit:
https://sourceware.org/git/?p=glibc.git;a=commit;h=ceb9e56b3d1f8c1922e0526c2e841373843460e2
and related issue:
https://sourceware.org/bugzilla/show_bug.cgi?id=14210.

build_msvc/bitcoin_config.h

@@ -41,9 +41,6 @@
 /* Define to 1 to enable ZMQ functions */
 #define ENABLE_ZMQ 1
 
-/* parameter and return value type for __fdelt_chk */
-/* #undef FDELT_TYPE */
-
 /* define if the Boost library is available */
 #define HAVE_BOOST /**/
 

configure.ac

@@ -717,22 +717,8 @@ AX_GCC_FUNC_ATTRIBUTE([dllexport])
 AX_GCC_FUNC_ATTRIBUTE([dllimport])
 
 if test x$use_glibc_compat != xno; then
-
+  AX_CHECK_LINK_FLAG([[-Wl,--wrap=__divmoddi4]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=__divmoddi4"])
-  dnl __fdelt_chk's params and return type have changed from long unsigned int to long int.
+  AX_CHECK_LINK_FLAG([[-Wl,--wrap=log2f]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=log2f"])
-  dnl See which one is present here.
-  AC_MSG_CHECKING(__fdelt_chk type)
-  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#ifdef _FORTIFY_SOURCE
-                    #undef _FORTIFY_SOURCE
-                  #endif
-                  #define _FORTIFY_SOURCE 2
-                  #include <sys/select.h>
-     extern "C" long unsigned int __fdelt_warn(long unsigned int);]],[[]])],
-    [ fdelt_type="long unsigned int"],
-    [ fdelt_type="long int"])
-  AC_MSG_RESULT($fdelt_type)
-  AC_DEFINE_UNQUOTED(FDELT_TYPE, $fdelt_type,[parameter and return value type for __fdelt_chk])
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=__divmoddi4]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=__divmoddi4"],, [[$LDFLAG_WERROR]])
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=log2f]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=log2f"],, [[$LDFLAG_WERROR]])
 else
   AC_SEARCH_LIBS([clock_gettime],[rt])
 fi

src/compat/glibc_compat.cpp

@@ -9,10 +9,6 @@
 #include <cstddef>
 #include <cstdint>
 
-#if defined(HAVE_SYS_SELECT_H)
-#include <sys/select.h>
-#endif
-
 // Prior to GLIBC_2.14, memcpy was aliased to memmove.
 extern "C" void* memmove(void* a, const void* b, size_t c);
 extern "C" void* memcpy(void* a, const void* b, size_t c)
@@ -20,15 +16,6 @@ extern "C" void* memcpy(void* a, const void* b, size_t c)
     return memmove(a, b, c);
 }
 
-extern "C" void __chk_fail(void) __attribute__((__noreturn__));
-extern "C" FDELT_TYPE __fdelt_warn(FDELT_TYPE a)
-{
-    if (a >= FD_SETSIZE)
-        __chk_fail();
-    return a / __NFDBITS;
-}
-extern "C" FDELT_TYPE __fdelt_chk(FDELT_TYPE) __attribute__((weak, alias("__fdelt_warn")));
-
 #if defined(__i386__) || defined(__arm__)
 
 extern "C" int64_t __udivmoddi4(uint64_t u, uint64_t v, uint64_t* rp);