Makefile: don't override environment's SPHINXBUILD or NAILING_CARGO

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/Makefile b/Makefile
index 36f13aafb5eaae08b09cd145e3e4fa6bce154991..29367ce7999d5f10e093143d7a9ad95601a74dc2 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -49,7 +49,7 @@ WASM_BINDGEN_OPTIONS =                                                \
 
 BUNDLE_SOURCES ?= bundle-rust-sources
 
-SPHINXBUILD   = sphinx-build
+SPHINXBUILD   ?= sphinx-build
 
 ifndef INKSCAPE_EXTENSIONS
 INKSCAPE ?= inkscape
@@ -70,7 +70,7 @@ PUBLISHED_BRANCH=published
 
 ifneq (,$(wildcard ../Cargo.nail))
 
-NAILING_CARGO = nailing-cargo
+NAILING_CARGO ?= nailing-cargo
 CARGO = $(NAILING_CARGO)
 BUILD_SUBDIR ?= ../Build
 TARGET_DIR = $(BUILD_SUBDIR)/$(notdir $(PWD))/target