Bug 1392643 Turn on c++14 for MinGW globally r=bagder,froydnj

Technically this turns on gnu++14. I encountered a few errors when using c++14:
1) _USE_MATH_DEFINES needed to be defined for MinGW
2) MinGW did not define _finite under c++14
3) MinGW's float.h did not define Microsoft specific float functions under c++14

All of these were because c++14 defines _STRICT_ANSI_ which MinGW obeys and
avoids defining certain functions. The first two could be patched around, but
the third was a blocker, so we switched to gnu++14

MozReview-Commit-ID: 6Y7gEQgApYp

--HG--
extra : rebase_source : dabbd40c049c36e780b585e0bef0a8e25887d089

build/moz.configure/toolchain.configure

@@ -374,13 +374,24 @@ def check_compiler(compiler, language, target):
     # Note: MSVC, while supporting C++11, still reports 199711L for __cplusplus.
     # Note: this is a strict version check because we used to always add
     # -std=gnu++11.
+    draft_cxx14_version = 201300
+    cxx14_version = 201402
     if info.language == 'C++':
-        if info.type in ('clang', 'gcc') and info.language_version != 201103:
-            append_flag('-std=gnu++11')
-        # MSVC 2015 headers include C++14 features, but don't guard them
-        # with appropriate checks.
-        if info.type == 'clang-cl' and info.language_version != 201402:
-            append_flag('-std=c++14')
+        if target.kernel != 'WINNT':
+            if info.type in ('clang', 'gcc') and info.language_version != 201103:
+                append_flag('-std=gnu++11')
+        else:
+            if info.type == 'clang' and info.language_version != 201103:
+                append_flag('-std=gnu++11')
+            # MSVC 2015 headers include C++14 features, but don't guard them
+            # with appropriate checks.
+            if info.type == 'clang-cl' and info.language_version != cxx14_version:
+                append_flag('-std=c++14')
+            # GCC 4.9 indicates that it implements draft C++14 features
+            # instead of the full language.
+            elif info.type == 'gcc' and not \
+                (info.language_version == draft_cxx14_version or info.language_version == cxx14_version):
+                append_flag('-std=gnu++14')
 
     # We force clang-cl to emulate Visual C++ 2015 Update 3.
     if info.type == 'clang-cl' and info.version != '19.00.24213':

python/mozbuild/mozbuild/test/configure/test_toolchain_configure.py

@@ -37,6 +37,10 @@ DEFAULT_CXX_11 = {
     '__cplusplus': '201103L',
 }
 
+DRAFT_CXX_14 = {
+    '__cplusplus': '201300L',
+}
+
 DEFAULT_CXX_14 = {
     '__cplusplus': '201402L',
 }
@@ -49,6 +53,10 @@ SUPPORTS_GNUXX11 = {
     '-std=gnu++11': DEFAULT_CXX_11,
 }
 
+SUPPORTS_GNUXX14 = {
+    '-std=gnu++14': DEFAULT_CXX_14,
+}
+
 SUPPORTS_CXX14 = {
     '-std=c++14': DEFAULT_CXX_14,
 }
@@ -76,13 +84,16 @@ def GCC(version):
 def GXX(version):
     return GCC_BASE(version) + DEFAULT_CXX_97 + SUPPORTS_GNUXX11
 
+SUPPORTS_DRAFT_CXX14_VERSION = {
+    '-std=gnu++14': DRAFT_CXX_14,
+}
 
 GCC_4_7 = GCC('4.7.3')
 GXX_4_7 = GXX('4.7.3')
 GCC_4_9 = GCC('4.9.3')
-GXX_4_9 = GXX('4.9.3')
+GXX_4_9 = GXX('4.9.3') + SUPPORTS_DRAFT_CXX14_VERSION
 GCC_5 = GCC('5.2.1') + DEFAULT_C11
-GXX_5 = GXX('5.2.1')
+GXX_5 = GXX('5.2.1') + SUPPORTS_GNUXX14
 
 GCC_PLATFORM_LITTLE_ENDIAN = {
     '__BYTE_ORDER__': 1234,
@@ -163,7 +174,7 @@ def CLANG(version):
 @memoize
 def CLANGXX(version):
     return (GCC_BASE('4.2.1') + CLANG_BASE(version) + DEFAULT_CXX_97 +
-            SUPPORTS_GNUXX11)
+            SUPPORTS_GNUXX11 + SUPPORTS_GNUXX14)
 
 
 CLANG_3_3 = CLANG('3.3.0') + DEFAULT_C99
@@ -173,6 +184,9 @@ CLANGXX_3_6 = CLANGXX('3.6.2') + {
     '-std=gnu++11': {
         '__has_feature(cxx_alignof)': '1',
     },
+    '-std=gnu++14': {
+        '__has_feature(cxx_alignof)': '1',
+    },
 }
 
 
@@ -901,9 +915,21 @@ class WindowsToolchainTest(BaseToolchainTest):
     CLANGXX_3_6_RESULT = LinuxToolchainTest.CLANGXX_3_6_RESULT
     GCC_4_7_RESULT = LinuxToolchainTest.GCC_4_7_RESULT
     GCC_4_9_RESULT = LinuxToolchainTest.GCC_4_9_RESULT
-    GXX_4_9_RESULT = LinuxToolchainTest.GXX_4_9_RESULT
+    GXX_4_9_RESULT = CompilerResult(
+        flags=['-std=gnu++14'],
+        version='4.9.3',
+        type='gcc',
+        compiler='/usr/bin/g++',
+        language='C++',
+    )
     GCC_5_RESULT = LinuxToolchainTest.GCC_5_RESULT
-    GXX_5_RESULT = LinuxToolchainTest.GXX_5_RESULT
+    GXX_5_RESULT = CompilerResult(
+        flags=['-std=gnu++14'],
+        version='5.2.1',
+        type='gcc',
+        compiler='/usr/bin/g++-5',
+        language='C++',
+    )
 
     # VS2015u3 or greater is required.
     def test_msvc(self):