external/Makefile: Change variable HOST to MAKE_HOST

Proposed fix for issue ElementsProject#1231 - FreeBSD (tcsh) build problem due
to HOST environment variable.

The variable is used for cross-compilation. The process may be
improved even further in the future. So far this hot fix.

doc/INSTALL.md

@@ -233,7 +233,7 @@ This will allow you to properly configure
 the build for the target device environment.
 Build with:
 
-    BUILD=x86_64 HOST=arm-linux-androideabi \
+    BUILD=x86_64 MAKE_HOST=arm-linux-androideabi \
       make PIE=1 DEVELOPER=0 \
       CONFIGURATOR_CC="arm-linux-androideabi-clang -static"
 
@@ -257,13 +257,13 @@ Depending on your toolchain location and target arch, source env variables will
 Install the `qemu-user` package. This will allow you to properly configure the build for the target device environment. Then, build with the following commands. (A 64-bit build system is assumed here.)
 
     make CC=gcc clean ccan/tools/configurator/configurator
-    BUILD=x86_64 HOST=arm-linux-gnueabihf make PIE=1 DEVELOPER=0 CONFIGURATOR_CC="arm-linux-gnueabihf-gcc -static" LDFLAGS="-L/path/to/gmp-and-sqlite/lib" CFLAGS="-std=gnu11 -I /path/to/gmp-and-sqlite/include -I . -I ccan -I external/libwally-core/src/secp256k1/include -I external/libsodium/src/libsodium/include -I external/jsmn -I external/libwally-core/include -I external/libbacktrace -I external/libbase58"
+    BUILD=x86_64 MAKE_HOST=arm-linux-gnueabihf make PIE=1 DEVELOPER=0 CONFIGURATOR_CC="arm-linux-gnueabihf-gcc -static" LDFLAGS="-L/path/to/gmp-and-sqlite/lib" CFLAGS="-std=gnu11 -I /path/to/gmp-and-sqlite/include -I . -I ccan -I external/libwally-core/src/secp256k1/include -I external/libsodium/src/libsodium/include -I external/jsmn -I external/libwally-core/include -I external/libbacktrace -I external/libbase58"
 
 The compilation will eventually fail due to a compile error in the `cdump` CCAN module. Recompile the module, and then re-run the make system.
 
     make clean -C ccan/ccan/cdump/tools
     make CC=gcc -C ccan/ccan/cdump/tools
-    BUILD=x86_64 HOST=arm-linux-gnueabihf make PIE=1 DEVELOPER=0 CONFIGURATOR_CC="arm-linux-gnueabihf-gcc -static" LDFLAGS="-L/path/to/gmp-and-sqlite/lib" CFLAGS="-std=gnu11 -I /path/to/gmp-and-sqlite/include -I . -I ccan -I external/libwally-core/src/secp256k1/include -I external/libsodium/src/libsodium/include -I external/jsmn -I external/libwally-core/include -I external/libbacktrace -I external/libbase58"
+    BUILD=x86_64 MAKE_HOST=arm-linux-gnueabihf make PIE=1 DEVELOPER=0 CONFIGURATOR_CC="arm-linux-gnueabihf-gcc -static" LDFLAGS="-L/path/to/gmp-and-sqlite/lib" CFLAGS="-std=gnu11 -I /path/to/gmp-and-sqlite/include -I . -I ccan -I external/libwally-core/src/secp256k1/include -I external/libsodium/src/libsodium/include -I external/jsmn -I external/libwally-core/include -I external/libbacktrace -I external/libbase58"
 
 Additional steps
 --------------------

external/Makefile

@@ -32,7 +32,7 @@ external/libsodium.a: external/libsodium/src/libsodium/libsodium.la
 external/libsodium/src/libsodium/include/sodium.h: submodcheck-libsodium
 
 external/libsodium/src/libsodium/libsodium.la: external/libsodium/src/libsodium/include/sodium.h
-	cd external/libsodium && ./autogen.sh && ./configure CC="$(CC)" --enable-static=yes --host="$(HOST)" --build="$(BUILD)" --enable-shared=no --enable-tests=no --prefix=/ --libdir=/ && $(MAKE)
+	cd external/libsodium && ./autogen.sh && ./configure CC="$(CC)" --enable-static=yes --host="$(MAKE_HOST)" --build="$(BUILD)" --enable-shared=no --enable-tests=no --prefix=/ --libdir=/ && $(MAKE)
 
 $(LIBWALLY_HEADERS) $(LIBSECP_HEADERS): submodcheck-libwally-core
 
@@ -42,7 +42,7 @@ external/libsecp256k1.% external/libwallycore.%: external/libwally-core/src/secp
 	$(MAKE) -C external/libwally-core DESTDIR=$$(pwd)/external install-exec
 
 external/libwally-core/src/libwallycore.% external/libwally-core/src/secp256k1/libsecp256k1.%: $(LIBWALLY_HEADERS) $(LIBSECP_HEADERS)
-	cd external/libwally-core && ./tools/autogen.sh && ./configure CC="$(CC)" --enable-static=yes --host="$(HOST)" --build="$(BUILD)" --enable-module-recovery --enable-shared=no --prefix=/ --libdir=/ && $(MAKE)
+	cd external/libwally-core && ./tools/autogen.sh && ./configure CC="$(CC)" --enable-static=yes --host="$(MAKE_HOST)" --build="$(BUILD)" --enable-module-recovery --enable-shared=no --prefix=/ --libdir=/ && $(MAKE)
 
 external/jsmn/jsmn.h: submodcheck-jsmn
 
@@ -75,7 +75,7 @@ external/libbacktrace/backtrace.h: submodcheck-libbacktrace
 # Need separate build dir: changes inside submodule make git think it's dirty.
 external/libbacktrace.a: external/libbacktrace/backtrace.h
 	@mkdir external/libbacktrace-build 2>/dev/null || true
-	cd external/libbacktrace-build && ../libbacktrace/configure CC="$(CC)" --enable-static=yes --host="$(HOST)" --build="$(BUILD)" --enable-shared=no --prefix=/ --libdir=/ && $(MAKE)
+	cd external/libbacktrace-build && ../libbacktrace/configure CC="$(CC)" --enable-static=yes --host="$(MAKE_HOST)" --build="$(BUILD)" --enable-shared=no --prefix=/ --libdir=/ && $(MAKE)
 	$(MAKE) -C external/libbacktrace-build DESTDIR=$$(pwd)/external install-exec
 
 distclean: external-distclean