build: Disable Visual Studio warning "conditional expression is constant"

- Disable warning C4127 "conditional expression is constant" globally
  in curl_setup.h for when building with Microsoft's compiler.

This mainly affects building with the Visual Studio project files found
in the projects dir.

Prior to this change the cmake and winbuild build systems already
disabled 4127 globally for when building with Microsoft's compiler.
Also, 4127 was already disabled for all build systems in the limited
circumstance of the WHILE_FALSE macro which disabled the warning
specifically for while(0). This commit removes the WHILE_FALSE macro and
all other cruft in favor of disabling globally in curl_setup.

Background:

We have various macros that cause 0 or 1 to be evaluated, which would
cause warning C4127 in Visual Studio. For example this causes it:

    #define Curl_resolver_asynch() 1

Full behavior is not clearly defined and inconsistent across versions.
However it is documented that since VS 2015 Update 3 Microsoft has
addressed this somewhat but not entirely, not warning on while(true) for
example.

Prior to this change some C4127 warnings occurred when I built with
Visual Studio using the generated projects in the projects dir.

Closes https://github.com/curl/curl/pull/4658

1 files changed, 2 insertions, 23 deletions

diff --git a/lib/curl_setup_once.h b/lib/curl_setup_once.h
index 413ccea91..9d504cb6e 100644
--- a/lib/curl_setup_once.h
+++ b/lib/curl_setup_once.h
@@ -330,27 +330,6 @@ struct timeval {
 #include "curl_ctype.h"
 
 /*
- * Macro WHILE_FALSE may be used to build single-iteration do-while loops,
- * avoiding compiler warnings. Mostly intended for other macro definitions.
- */
-
-#define WHILE_FALSE  while(0)
-
-#if defined(_MSC_VER) && !defined(__POCC__)
-#  undef WHILE_FALSE
-#  if (_MSC_VER < 1500)
-#    define WHILE_FALSE  while(1, 0)
-#  else
-#    define WHILE_FALSE \
-__pragma(warning(push)) \
-__pragma(warning(disable:4127)) \
-while(0) \
-__pragma(warning(pop))
-#  endif
-#endif
-
-
-/*
  * Typedef to 'int' if sig_atomic_t is not an available 'typedefed' type.
  */
 
@@ -387,7 +366,7 @@ typedef int sig_atomic_t;
 #ifdef DEBUGBUILD
 #define DEBUGF(x) x
 #else
-#define DEBUGF(x) do { } WHILE_FALSE
+#define DEBUGF(x) do { } while(0)
 #endif
 
 
@@ -398,7 +377,7 @@ typedef int sig_atomic_t;
 #if defined(DEBUGBUILD) && defined(HAVE_ASSERT_H)
 #define DEBUGASSERT(x) assert(x)
 #else
-#define DEBUGASSERT(x) do { } WHILE_FALSE
+#define DEBUGASSERT(x) do { } while(0)
 #endif