Added ".syntax unified"

Otherwise gcc complains. I've tested this to work with the normal CMakeLists.txt provided in a few examples.

src/rp2_common/hardware_clocks/clocks.c

@@ -78,6 +78,7 @@ bool clock_configure(enum clock_index clk_index, uint32_t src, uint32_t auxsrc,
             // necessarily running, nor is timer... so, 3 cycles per loop:
             uint delay_cyc = configured_freq[clk_sys] / configured_freq[clk_index] + 1;
             asm volatile (
+                ".syntax unified \n\t"
                 "1: \n\t"
                 "subs %0, #1 \n\t"
                 "bne 1b"