Merge bitcoin#30590: build: Remove unused visibility checks

bbcba09 build: remove check for __declspec(dllexport) (fanquake)
37c9abd build: remove check for __attribute__((visibility.. (fanquake)

Pull request description:

  These are unused (since libbitcoinconsensus / bitcoin#29648), and the current CMake port doesn't quite match behaviour, such that there's no real point in doing the check. So rather than port anything, just remove it. If these are needed again in future (i.e for kernel or similar), they can be revisted, and it might be the case that build-system level checks will not be wanted.

ACKs for top commit:
  hebasto:
    ACK bbcba09. I've verified that neither `HAVE_DEFAULT_VISIBILITY_ATTRIBUTE` nor `HAVE_DLLEXPORT_ATTRIBUTE` are used or evaluated in the current codebase.
  TheCharlatan:
    ACK bbcba09
  willcl-ark:
    ACK bbcba09

Tree-SHA512: 332f018c50a159d2cbfd2f9ce018538fa11cf06a94e27ed42146945b86645af5881095df39cadd2f775a8ae348ebfc949d54f7eb4b62264bf48119c9f9952c20

Author: fanquake

build_msvc/bitcoin_config.h.in

@@ -49,9 +49,6 @@
    */
 #define HAVE_DECL_SETSID 0
 
-/* Define if the dllexport attribute is supported. */
-#define HAVE_DLLEXPORT_ATTRIBUTE 1
-
 /* Define to the address where bug reports for this package should be sent. */
 #define PACKAGE_BUGREPORT "https://github.com/bitcoin/bitcoin/issues"
 

configure.ac

@@ -943,35 +943,6 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
  [ AC_MSG_RESULT([no])]
 )
 
-AC_MSG_CHECKING([for default visibility attribute])
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([
-  int foo(void) __attribute__((visibility("default")));
-  int main(){}
-  ])],
-  [
-    AC_DEFINE([HAVE_DEFAULT_VISIBILITY_ATTRIBUTE], [1], [Define if the visibility attribute is supported.])
-    AC_MSG_RESULT([yes])
-  ],
-  [
-    AC_MSG_RESULT([no])
-    if test "$use_reduce_exports" = "yes"; then
-      AC_MSG_ERROR([Cannot find a working visibility attribute. Use --disable-reduce-exports.])
-    fi
-  ]
-)
-
-AC_MSG_CHECKING([for dllexport attribute])
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([
-  __declspec(dllexport) int foo(void);
-  int main(){}
-  ])],
-  [
-    AC_DEFINE([HAVE_DLLEXPORT_ATTRIBUTE], [1], [Define if the dllexport attribute is supported.])
-    AC_MSG_RESULT([yes])
-  ],
-  [AC_MSG_RESULT([no])]
-)
-
 dnl Check for different ways of gathering OS randomness
 AC_MSG_CHECKING([for Linux getrandom function])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[