diff --git a/include/boost/config/compiler/clang.hpp b/include/boost/config/compiler/clang.hpp
index 0fdf331f..da736bc4 100644
--- a/include/boost/config/compiler/clang.hpp
+++ b/include/boost/config/compiler/clang.hpp
@@ -98,11 +98,15 @@
 //
 // Dynamic shared object (DSO) and dynamic-link library (DLL) support
 //
-#if !defined(_WIN32) && !defined(__WIN32__) && !defined(WIN32)
+#if defined(_WIN32) || defined(__WIN32__) || defined(WIN32) || defined(__CYGWIN__)
+#  define BOOST_HAS_DECLSPEC
+#  define BOOST_SYMBOL_EXPORT __attribute__((__dllexport__))
+#  define BOOST_SYMBOL_IMPORT __attribute__((__dllimport__))
+#else
 #  define BOOST_SYMBOL_EXPORT __attribute__((__visibility__("default")))
 #  define BOOST_SYMBOL_IMPORT
-#  define BOOST_SYMBOL_VISIBLE __attribute__((__visibility__("default")))
 #endif
+#define BOOST_SYMBOL_VISIBLE __attribute__((__visibility__("default")))
 
 //
 // The BOOST_FALLTHROUGH macro can be used to annotate implicit fall-through
diff --git a/include/boost/config/compiler/gcc.hpp b/include/boost/config/compiler/gcc.hpp
index 8296520a..4fe968a0 100644
--- a/include/boost/config/compiler/gcc.hpp
+++ b/include/boost/config/compiler/gcc.hpp
@@ -99,10 +99,10 @@
 // Dynamic shared object (DSO) and dynamic-link library (DLL) support
 //
 #if __GNUC__ >= 4
-#  if (defined(_WIN32) || defined(__WIN32__) || defined(WIN32)) && !defined(__CYGWIN__)
+#  if defined(_WIN32) || defined(__WIN32__) || defined(WIN32) || defined(__CYGWIN__)
      // All Win32 development environments, including 64-bit Windows and MinGW, define
      // _WIN32 or one of its variant spellings. Note that Cygwin is a POSIX environment,
-     // so does not define _WIN32 or its variants.
+     // so does not define _WIN32 or its variants, but still supports dllexport/dllimport.
 #    define BOOST_HAS_DECLSPEC
 #    define BOOST_SYMBOL_EXPORT __attribute__((__dllexport__))
 #    define BOOST_SYMBOL_IMPORT __attribute__((__dllimport__))
diff --git a/include/boost/config/compiler/intel.hpp b/include/boost/config/compiler/intel.hpp
index 00396b03..0eea05b9 100644
--- a/include/boost/config/compiler/intel.hpp
+++ b/include/boost/config/compiler/intel.hpp
@@ -45,6 +45,7 @@
 
 #undef BOOST_GCC_VERSION
 #undef BOOST_GCC_CXX11
+#undef BOOST_GCC
 
 // Broken in all versions up to 17 (newer versions not tested)
 #if (__INTEL_COMPILER <= 1700) && !defined(BOOST_NO_CXX14_CONSTEXPR)
diff --git a/include/boost/cstdint.hpp b/include/boost/cstdint.hpp
index 0b169132..c8474c46 100644
--- a/include/boost/cstdint.hpp
+++ b/include/boost/cstdint.hpp
@@ -34,6 +34,17 @@
 #endif
 
 #include <boost/config.hpp>
+//
+// For the following code we get several warnings along the lines of:
+//
+// boost/cstdint.hpp:428:35: error: use of C99 long long integer constant
+//
+// So we declare this a system header to suppress these warnings.
+// See also https://github.com/boostorg/config/issues/190
+//
+#if defined(__GNUC__) && (__GNUC__ >= 4)
+#pragma GCC system_header
+#endif
 
 //
 // Note that GLIBC is a bit inconsistent about whether int64_t is defined or not
@@ -408,16 +419,6 @@ INT#_C macros if they're not already defined (John Maddock).
 #if !defined(BOOST__STDC_CONSTANT_MACROS_DEFINED) && \
    (!defined(INT8_C) || !defined(INT16_C) || !defined(INT32_C) || !defined(INT64_C))
 //
-// For the following code we get several warnings along the lines of:
-//
-// boost/cstdint.hpp:428:35: error: use of C99 long long integer constant
-//
-// So we declare this a system header to suppress these warnings.
-//
-#if defined(__GNUC__) && (__GNUC__ >= 4)
-#pragma GCC system_header
-#endif
-//
 // Undef the macros as a precaution, since we may get here if <stdint.h> has failed
 // to define them all, see https://svn.boost.org/trac/boost/ticket/12786
 //