Build examples last

Examples are "leaf" packages, that pull some other packages. So build
the other packages first to get and fix all the errors there, before
building the examples.

Makefile

@@ -18,7 +18,7 @@ TOOLS_MOD_DIR := ./internal/tools
 # All source code and documents. Used in spell check.
 ALL_DOCS := $(shell find . -name '*.md' -type f | sort)
 # All directories with go.mod files related to opentelemetry library. Used for building, testing and linting.
-ALL_GO_MOD_DIRS := $(filter-out $(TOOLS_MOD_DIR), $(shell find . -type f -name 'go.mod' -exec dirname {} \; | sort))
+ALL_GO_MOD_DIRS := $(filter-out $(TOOLS_MOD_DIR), $(shell find . -type f -name 'go.mod' -exec dirname {} \; | egrep -v '^./example' | sort)) $(shell find ./example -type f -name 'go.mod' -exec dirname {} \; | sort)
 ALL_COVERAGE_MOD_DIRS := $(shell find . -type f -name 'go.mod' -exec dirname {} \; | egrep -v '^./example|^$(TOOLS_MOD_DIR)' | sort)
 
 # Mac OS Catalina 10.5.x doesn't support 386. Hence skip 386 test