We currently write a mix of "if (FOO)" and "if(FOO)". While the former looks
more like a usual language, CMake believes everything, even "if" and "else", is
just a really really funny function call (a "command").

We should pick something for consistency. Upstream CMake writes "if(FOO)", so
go with that one.

Change-Id: I67e0eb650a52670110b417312a362c9f161c8721
Reviewed-on: https://boringssl-review.googlesource.com/30807
Reviewed-by: Adam Langley <agl@google.com>