Obtain SANDMARK_CUSTOM_NAME from variant name and make it optional

But, also allow overriding it using an environment variable, if required.

Closes ocaml-bench#347

Makefile

@@ -32,9 +32,6 @@ SANDMARK_REMOVE_PACKAGES ?= ""
 # Default list of packages to override
 SANDMARK_OVERRIDE_PACKAGES ?= ""
 
-# Override orun with custom name
-SANDMARK_CUSTOM_NAME ?= ""
-
 # Flag to select whether to use sys_dune_hack
 USE_SYS_DUNE_HACK ?= 0
 
@@ -213,6 +210,7 @@ blah:
 	@echo ${PACKAGES}
 
 ocaml-versions/%.bench: depend override_packages/% log_sandmark_hash ocaml-versions/%.json .FORCE
+	$(eval SANDMARK_CUSTOM_NAME ?= $*)
 	$(eval CONFIG_SWITCH_NAME = $*)
 	$(eval CONFIG_OPTIONS      = $(shell jq -r '.configure // empty' ocaml-versions/$*.json))
 	$(eval CONFIG_RUN_PARAMS   = $(shell jq -r '.runparams // empty' ocaml-versions/$*.json))

README.md

@@ -369,6 +369,7 @@ work on OS X is to install GNU sed with homebrew and then update the
 | PRE_BENCH_EXEC | Any specific commands that needed to be executed before the benchmark. For eg. `PRE_BENCH_EXEC='taskset --cpu-list 3 setarch uname -m --addr-no-randomize'` | null string | executing benchmark | RUN_BENCH_TARGET | The executable to be used to run the benchmarks | `run_orun` | executing benchmark |
 | RUN_BENCH_TARGET | The executable to be used to run the benchmarks | `run_orun` | executing benchmark |
 | RUN_CONFIG_JSON | Input file selection that contains the list of benchmarks | `run_config.json` | executing benchmark |
+| SANDMARK_CUSTOM_NAME | Custom name to use for the bench output file | variant from the `ocaml-version/<variant>.json` file name | executing benchmark |
 | SANDMARK_DUNE_VERSION | Default dune version to be used | 2.9.0 | building compiler and its dependencies |
 | SANDMARK_OVERRIDE_PACKAGES | A list of dependency packages with versions that can be overrided (optional) | "" | building compiler and its dependencies |
 | SANDMARK_REMOVE_PACKAGES | A list of dependency packages to be dynamically removed (optional) | "" | building compiler and its dependencies |