Increase warning level & Fix all warnings

As discussed in !357 (merged), we should increase the number of enabled compiler warnings to catch a lot more silent bugs. Increase the meson-global warning level to 2, but excluding the unused-parameter and old-style-declaration warnings. Additionally, disable warnings for libraries as we cannot fix that code anyway.

Fixes #192 (closed)

Cc: @fuchsi

hw-tests/ecgtest/main.c

@@ -401,11 +401,11 @@ int main(void)
 
 	uint32_t ecgFIFO, readECGSamples, idx, ETAG[32], status;
 	int16_t ecgSample[32];
-	const int EINT_STATUS_MASK       = 1 << 23;
-	const int FIFO_OVF_MASK          = 0x7;
-	const int FIFO_VALID_SAMPLE_MASK = 0x0;
-	const int FIFO_FAST_SAMPLE_MASK  = 0x1;
-	const int ETAG_BITS_MASK         = 0x7;
+	const uint32_t EINT_STATUS_MASK       = 1 << 23;
+	const uint32_t FIFO_OVF_MASK          = 0x7;
+	const uint32_t FIFO_VALID_SAMPLE_MASK = 0x0;
+	const uint32_t FIFO_FAST_SAMPLE_MASK  = 0x1;
+	const uint32_t ETAG_BITS_MASK         = 0x7;
 
 	while (1) {
 #if 1