fix: correct Makefile syntax and variable usage in eslint rules

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: na
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: na
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: na
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: na
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: Planeshifter

tools/make/lib/lint/javascript/eslint.mk

@@ -66,7 +66,7 @@ endif
 endif
 
 # Append user-supplied command-line options:
-eslint_flags += ESLINT_FLAGS
+eslint_flags += $(ESLINT_FLAGS)
 
 # RULES #
 
@@ -256,6 +256,7 @@ ifeq ($(FAIL_FAST), true)
 		echo ''; \
 		echo "Linting file: $$file"; \
 		$(ESLINT) $(eslint_flags) --config $(ESLINT_CONF) $$file || exit 1; \
+	done
 else
 	$(QUIET) status=0; \
 	for file in $(FILES); do \