make all non hardware_ libraries foo add C preprocessor definition LIB_FOO=1, and remove bespoke definitions which were all undocumented anyway (#374)

src/rp2_common/pico_stdlib/CMakeLists.txt

@@ -6,7 +6,7 @@ option(PICO_STDIO_USB "Globablly enable stdio USB" 0)
 option(PICO_STDIO_USB "Globablly enable stdio semihosting " 0)
 
 if (NOT TARGET pico_stdlib)
-    add_library(pico_stdlib INTERFACE)
+    pico_add_impl_library(pico_stdlib)
     target_sources(pico_stdlib INTERFACE
             ${CMAKE_CURRENT_LIST_DIR}/stdlib.c
     )

src/rp2_common/pico_stdlib/stdlib.c

@@ -7,7 +7,7 @@
 #include "pico/stdlib.h"
 #include "hardware/pll.h"
 #include "hardware/clocks.h"
-#if PICO_STDIO_UART
+#if LIB_PICO_STDIO_UART
 #include "pico/stdio_uart.h"
 #else
 #include "pico/binary_info.h"
@@ -90,7 +90,7 @@ bool check_sys_clock_khz(uint32_t freq_khz, uint *vco_out, uint *postdiv1_out, u
 }
 
 void setup_default_uart() {
-#if PICO_STDIO_UART
+#if LIB_PICO_STDIO_UART
     stdio_uart_init();
 #elif defined(PICO_DEFAULT_UART_BAUD_RATE) && defined(PICO_DEFAULT_UART_TX_PIN) && defined(PICO_DEFAULT_UART_RX_PIN)
     // this is mostly for backwards compatibility - stdio_uart_init is a bit more nuanced, and usually likely to be present