gh-157695: Parse also _Py_HAVE_xxx variables in sysconfig

[vstinner]

Add parse_config_h() tests in test_sysconfig.

• Issue: The Python C API should only define macros with a name starting wit Py #157695

[vstinner]

Example of build/lib.linux-x86_64-3.16/_sysconfigdata_td_linux_x86_64-linux-gnu.py changes on my Linux box:

--- main.py	2026-10-06 20:47:16.919435265 +0200
+++ change.py	2026-10-06 20:47:36.828550161 +0200
@@ -1150,6 +1150,25 @@
     'X87_DOUBLE_ROUNDING': 0,
     'XMLLIBSUBDIRS': 'xml xml/dom xml/etree xml/parsers xml/sax',
     'ZIP_STDLIB': 'python3.16t.zip',
+    '_Py_FFI_SUPPORT_C_COMPLEX': 1,
+    '_Py_HACL_CAN_COMPILE_VEC128': 1,
+    '_Py_HACL_CAN_COMPILE_VEC256': 1,
+    '_Py_HAVE_ACOSPI': 1,
+    '_Py_HAVE_ASINPI': 1,
+    '_Py_HAVE_ATAN2PI': 1,
+    '_Py_HAVE_ATANPI': 1,
+    '_Py_HAVE_COSPI': 1,
+    '_Py_HAVE_EFFICIENT_BUILTIN_SHUFFLEVECTOR': 1,
+    '_Py_HAVE_FLOAT16': 1,
+    '_Py_HAVE_ICONV': 1,
+    '_Py_HAVE_LIBGCC_EH_FRAME_REGISTRATION': 1,
+    '_Py_HAVE_PR_SET_VMA_ANON_NAME': 1,
+    '_Py_HAVE_SINPI': 1,
+    '_Py_HAVE_TANPI': 1,
+    '_Py_LINKER_THREAD_STACK_SIZE': 0,
+    '_Py_STACK_GROWS_DOWN': 1,
+    '_Py_TAIL_CALL_INTERP': 0,
+    '_Py_WITH_FRAME_POINTERS': 1,
     'abs_builddir': '/home/vstinner/python/main',
     'abs_srcdir': '/home/vstinner/python/main',
     'datarootdir': '/usr/local/share',