Reworked how multi-layered defines work in the test-runner

In the test-runner, defines are parameterized constants (limited
to integers) that are generated from the test suite tomls resulting
in many permutations of each test.

In order to make this efficient, these defines are implemented as
multi-layered lookup tables, using per-layer/per-scope indirect
mappings. This lets the test-runner and test suites define their
own defines with compile-time indexes independently. It also makes
building of the lookup tables very efficient, since they can be
incrementally populated as we expand the test permutations.

The four current define layers and when we need to build them:

layer                           defines         predefine_map   define_map
user-provided overrides         per-run         per-run         per-suite
per-permutation defines         per-perm        per-case        per-perm
per-geometry defines            per-perm        compile-time    -
default defines                 compile-time    compile-time    -

.gitignore

@@ -14,3 +14,4 @@ test.c
 tests/*.toml.*
 scripts/__pycache__
 .gdb_history
+runners/test_runner

Makefile

@@ -54,6 +54,9 @@ override CFLAGS += -I.
 override CFLAGS += -std=c99 -Wall -pedantic
 override CFLAGS += -Wextra -Wshadow -Wjump-misses-init -Wundef
 
+override TESTFLAGS_ += -b
+# forward -j flag
+override TESTFLAGS_ += $(filter -j%,$(MAKEFLAGS))
 ifdef VERBOSE
 override TESTFLAGS     += -v
 override CALLSFLAGS    += -v
@@ -88,8 +91,6 @@ endif
 ifneq ($(OBJDUMP),objdump)
 override STRUCTSFLAGS += --objdump-tool="$(OBJDUMP)"
 endif
-# forward -j flag
-override TESTFLAGS_ += $(filter -j%,$(MAKEFLAGS))
 
 
 # commands