Revert "build: Fix undefined reference to __mulodi4"

This reverts commit e4c8bb62e4.

build-aux/m4/bitcoin_runtime_lib.m4

@@ -1,42 +0,0 @@
-# On some platforms clang builtin implementations
-# require compiler-rt as a runtime library to use.
-#
-# See:
-# - https://bugs.llvm.org/show_bug.cgi?id=28629
-
-m4_define([_CHECK_RUNTIME_testbody], [[
-  bool f(long long x, long long y, long long* p)
-  {
-    return __builtin_mul_overflow(x, y, p);
-  }
-  int main() { return 0; }
-]])
-
-AC_DEFUN([CHECK_RUNTIME_LIB], [
-
-  AC_LANG_PUSH([C++])
-
-  AC_MSG_CHECKING([for __builtin_mul_overflow])
-  AC_LINK_IFELSE(
-    [AC_LANG_SOURCE([_CHECK_RUNTIME_testbody])],
-    [
-      AC_MSG_RESULT([yes])
-      AC_DEFINE([HAVE_BUILTIN_MUL_OVERFLOW], [1], [Define if you have a working __builtin_mul_overflow])
-    ],
-    [
-      ax_check_save_flags="$LDFLAGS"
-      LDFLAGS="$LDFLAGS --rtlib=compiler-rt -lgcc_s"
-      AC_LINK_IFELSE(
-        [AC_LANG_SOURCE([_CHECK_RUNTIME_testbody])],
-        [
-          AC_MSG_RESULT([yes, with additional linker flags])
-          RUNTIME_LDFLAGS="--rtlib=compiler-rt -lgcc_s"
-          AC_DEFINE([HAVE_BUILTIN_MUL_OVERFLOW], [1], [Define if you have a working __builtin_mul_overflow])
-        ],
-        [AC_MSG_RESULT([no])])
-      LDFLAGS="$ax_check_save_flags"
-    ])
-
-  AC_LANG_POP
-  AC_SUBST([RUNTIME_LDFLAGS])
-])

configure.ac

@@ -1338,8 +1338,6 @@ if test "$enable_fuzz_binary" = "yes"; then
      ]],[[
       */ int not_main() {
      ]])])
-
-  CHECK_RUNTIME_LIB
 fi
 
 if test "$enable_wallet" != "no"; then

src/Makefile.test.include

@@ -240,7 +240,7 @@ if ENABLE_FUZZ_BINARY
 test_fuzz_fuzz_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) $(BOOST_CPPFLAGS)
 test_fuzz_fuzz_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 test_fuzz_fuzz_LDADD = $(FUZZ_SUITE_LD_COMMON)
-test_fuzz_fuzz_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS) $(PTHREAD_FLAGS) $(RUNTIME_LDFLAGS)
+test_fuzz_fuzz_LDFLAGS = $(RELDFLAGS) $(AM_LDFLAGS) $(LIBTOOL_APP_LDFLAGS) $(PTHREAD_FLAGS)
 test_fuzz_fuzz_SOURCES = \
  $(FUZZ_WALLET_SRC) \
  test/fuzz/addition_overflow.cpp \

src/test/fuzz/multiplication_overflow.cpp

@@ -2,10 +2,6 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#if defined(HAVE_CONFIG_H)
-#include <config/bitcoin-config.h>
-#endif
-
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
@@ -14,6 +10,14 @@
 #include <string>
 #include <vector>
 
+#if defined(__has_builtin)
+#if __has_builtin(__builtin_mul_overflow)
+#define HAVE_BUILTIN_MUL_OVERFLOW
+#endif
+#elif defined(__GNUC__)
+#define HAVE_BUILTIN_MUL_OVERFLOW
+#endif
+
 namespace {
 template <typename T>
 void TestMultiplicationOverflow(FuzzedDataProvider& fuzzed_data_provider)