build.go: introduce a friendlier way to build Ollama (#3548)

This commit introduces a more friendly way to build Ollama dependencies
and the binary without abusing `go generate` and removing the
unnecessary extra steps it brings with it.

This script also provides nicer feedback to the user about what is
happening during the build process.

At the end, it prints a helpful message to the user about what to do
next (e.g. run the new local Ollama).

llm/generate/gen_darwin.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
-# This script is intended to run inside the go generate
-# working directory must be ./llm/generate/
+# This script is intended to run inside the `go run build.go` script, which
+# sets the working directory to the correct location: ./llm/generate/.
 
 # TODO - add hardening to detect missing tools (cmake, etc.)
 
@@ -89,10 +89,10 @@ case "${GOARCH}" in
     ;;
 *)
     echo "GOARCH must be set"
-    echo "this script is meant to be run from within go generate"
+    echo "this script is meant to be run from within 'go run build.go'"
     exit 1
     ;;
 esac
 
 cleanup
-echo "go generate completed.  LLM runners: $(cd ${BUILD_DIR}/..; echo *)"
+echo "code generation completed.  LLM runners: $(cd ${BUILD_DIR}/..; echo *)"