hardware_adc_headers must depend on hardware_gpio_headers

[ooxi]

Since hardware/adc.h includes hardware/gpio.h, hardware_adc_headers must depend on hardware_gpio_headers

Fixes #975

[lurch]

Also links tangentially to #882 ?

[ooxi]

@lurch tangentially yes, but hardware_adc doesn't directly depend on hardware_gpio either (from CMakeLists.txt):

pico_simple_hardware_target(adc)

# additional library
target_link_libraries(hardware_adc INTERFACE hardware_resets)

[kilograham]

all dependencies issues are moving to 1.5.0

[kilograham]

closed in favor of #1211