missing -Wall -Wextra in subdirectories.

[rgetz]

Because the CFlags were set to 'private', they don't decend into the subdirectories, and all sorts of issues have leaked into the code base (most concerned about iiod). This change should be applied, and then all issues should be fixed.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5eee82f7..d7f90ec0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -211,7 +211,7 @@ elseif (CMAKE_COMPILER_IS_GNUCC)
        check_c_compiler_flag(-Wpedantic HAS_WPEDANTIC)
        check_c_compiler_flag(-Wshadow HAS_WSHADOW)

-       target_compile_options(iio PRIVATE -Wall -Wextra -Wno-unused-parameter
+       target_compile_options(iio PUBLIC -Wall -Wextra -Wno-unused-parameter
                $<$<BOOL:HAS_WPEDANTIC>:-Wpedantic>
                $<$<BOOL:HAS_WSHADOW>:-Wshadow>
        )