The cgo tool is enabled by default for native builds on systems where
it is expected to work. It is disabled by default when cross-compiling
as well as when the CC environment variable is unset and the default
C compiler (typically gcc or clang) cannot be found on the system PATH.
You can override the default by setting the CGO_ENABLED
environment variable when running the go tool: set it to 1 to enable

memory locations accessible to multiple goroutines.
</p>

<p>
Not introducing data races into race-free programs means not moving
writes out of conditional statements in which they appear.
For example, a compiler must not invert the conditional in this program:
</p>

<pre>
*p = 1
if cond {
	*p = 2
}
</pre>

<p>
That is, the compiler must not rewrite the program into this one:
</p>

<pre>
*p = 2