Python has way too many variables to control compiler flags:
---
# Compiler options
OPT=		@OPT@
BASECFLAGS=	@BASECFLAGS@
BASECPPFLAGS=	@BASECPPFLAGS@
CONFIGURE_CFLAGS=	@CFLAGS@
# CFLAGS_NODIST is used for building the interpreter and stdlib C extensions.
# Use it when a compiler flag should _not_ be part of the distutils CFLAGS
# once Python is installed (Issue #21121).
CONFIGURE_CFLAGS_NODIST=@CFLAGS_NODIST@
# LDFLAGS_NODIST is used in the same manner as CFLAGS_NODIST.
# Use it when a linker flag should _not_ be part of the distutils LDFLAGS
# once Python is installed (bpo-35257)
CONFIGURE_LDFLAGS_NODIST=@LDFLAGS_NODIST@
CONFIGURE_CPPFLAGS=	@CPPFLAGS@
CONFIGURE_LDFLAGS=	@LDFLAGS@
# Avoid assigning CFLAGS, LDFLAGS, etc. so users can use them on the
# command line to append to these values without stomping the pre-set
# values.
PY_CFLAGS=	$(BASECFLAGS) $(OPT) $(CONFIGURE_CFLAGS) $(CFLAGS) $(EXTRA_CFLAGS)
PY_CFLAGS_NODIST=$(CONFIGURE_CFLAGS_NODIST) $(CFLAGS_NODIST) -I$(srcdir)/Include/internal
# Both CPPFLAGS and LDFLAGS need to contain the shell's value for setup.py to
# be able to build extension modules using the directories specified in the
# environment variables
PY_CPPFLAGS=	$(BASECPPFLAGS) -I. -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS)
PY_LDFLAGS=	$(CONFIGURE_LDFLAGS) $(LDFLAGS)
PY_LDFLAGS_NODIST=$(CONFIGURE_LDFLAGS_NODIST) $(LDFLAGS_NODIST)
NO_AS_NEEDED=	@NO_AS_NEEDED@
SGI_ABI=	@SGI_ABI@
CCSHARED=	@CCSHARED@
# LINKFORSHARED are the flags passed to the $(CC) command that links
# the python executable -- this is only needed for a few systems
LINKFORSHARED=	@LINKFORSHARED@
ARFLAGS=	@ARFLAGS@
# Extra C flags added for building the interpreter object files.
CFLAGSFORSHARED=@CFLAGSFORSHARED@
# C flags used for building the interpreter object files
PY_STDMODULE_CFLAGS= $(PY_CFLAGS) $(PY_CFLAGS_NODIST) $(PY_CPPFLAGS) $(CFLAGSFORSHARED)
PY_BUILTIN_MODULE_CFLAGS= $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN
PY_CORE_CFLAGS=	$(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE
# Linker flags used for building the interpreter object files
PY_CORE_LDFLAGS=$(PY_LDFLAGS) $(PY_LDFLAGS_NODIST)
# Strict or non-strict aliasing flags used to compile dtoa.c, see above
CFLAGS_ALIASING=@CFLAGS_ALIASING@
---

I'm not sure which variables are "standard" and supposed to be overriden or not, because there is no documentation. The priority because these variables is not documented at all. For example:

* What the priority between BASECFLAGS, CFLAGS, OPT and EXTRA_FLAGS?
* Which flags are used to build Python core?
* Which flags are used to build modules of the standard library?
* Which flags are used to build third-party modules?

Linker flags are not documented neither which caused a regression for a short time (issue ith BLDSHARED if I recall correctly).

Examples of variables related to linker flags:

---
# LDFLAGS_NODIST is used in the same manner as CFLAGS_NODIST.
# Use it when a linker flag should _not_ be part of the distutils LDFLAGS
# once Python is installed (bpo-35257)
CONFIGURE_LDFLAGS_NODIST=@LDFLAGS_NODIST@
CONFIGURE_LDFLAGS=	@LDFLAGS@

PY_LDFLAGS=	$(CONFIGURE_LDFLAGS) $(LDFLAGS)
PY_LDFLAGS_NODIST=$(CONFIGURE_LDFLAGS_NODIST) $(LDFLAGS_NODIST)
PY_CORE_LDFLAGS=$(PY_LDFLAGS) $(PY_LDFLAGS_NODIST)

LDSHARED=	@LDSHARED@ $(PY_LDFLAGS)
BLDSHARED=	@BLDSHARED@ $(PY_CORE_LDFLAGS)
---