[wpimath] Suppress the -Wmaybe-uninitialized warning in Eigen (#3378)

GCC 11 emits a false positive when compiling Eigen and breaks the
build.

Fixes #3363.

wpimath/.styleguide

@@ -8,6 +8,10 @@ cppSrcFileInclude {
   \.cpp$
 }
 
+modifiableFileExclude {
+  \.patch$
+}
+
 generatedFileExclude {
   src/main/native/cpp/drake/
   src/main/native/eigeninclude/