libiconv: fix building with nvhpc (#43033)

var/spack/repos/builtin/packages/libiconv/package.py

@@ -41,6 +41,17 @@ def configure_args(self):
         args += self.enable_or_disable("libs")
         args.append("--with-pic")
 
+        # Starting version 1.17, libiconv uses the version of gnulib that implements a
+        # configure-time check for C compiler flags that enables/disables certain warning
+        # (see https://git.savannah.gnu.org/gitweb/?p=gnulib.git;h=0c8a563f6). Unfortunately, the
+        # check does not work for compilers that inject extra symbols into the translation unit
+        # during the preprocessing step. For example, NVHPC injects the definition of the
+        # __va_list_tag structure, which appears verbatim on the compilation command line as
+        # additional compiler flags. The easiest way to circumvent the issue is to make the
+        # configure script believe that the compiler does not support a flag that allows warnings:
+        if self.spec.satisfies("@1.17:%nvhpc"):
+            args.append("gl_cv_cc_wallow=none")
+
         # A hack to patch config.guess in the libcharset sub directory
         copy("./build-aux/config.guess", "libcharset/build-aux/config.guess")
         return args