compile with -mzos-target=zosv2r4 (#118)

Since v2r4 is the min supported OS.

Author: gabylb

BUILD.gn

@@ -13,6 +13,7 @@ config("zoslib_config") {
   cflags = [
     "-march=arch10",
     "-mtune=arch10",
+    "-mzos-target=zosv2r4",
     "-fno-short-enums",
     "-fzos-le-char-mode=ascii",
   ]

CMakeLists.txt

@@ -79,6 +79,7 @@ else()
     -fgnu-keywords
     -m64
     -march=arch10
+    -mzos-target=zosv2r4
     -fno-short-enums
     -fzos-le-char-mode=ascii)
 endif()

zoslib.gyp

@@ -31,7 +31,7 @@
           'cflags': ['-q64', '-qascii', '-qexportall', '-Wno-missing-field-initializers', '-qasmlib=//\\\'SYS1.MACLIB\\\''],
           'include_dirs': ['include'],
         }, {
-          'cflags': ['-fzos-le-char-mode=ascii', '-fgnu-keywords', '-fno-short-enums'],
+          'cflags': ['-fzos-le-char-mode=ascii', '-fgnu-keywords', '-fno-short-enums', '-mzos-target=zosv2r4'],
           'include_dirs': ['include', 'include/c++/v1'],
         }],
       ],