nanosvg: build implementation in extra c file

Speed up development iterations by building the nanosvg implementation
only once. Especially on the PinePhone it takes a bit.

src/meson.build

@@ -1,6 +1,7 @@
 src = [
-        'pbsplash.c',
         'animate.c',
+        'nanosvg.c',
+        'pbsplash.c',
 ]
 
 executable('pbsplash', src,

src/nanosvg.c

@@ -0,0 +1,9 @@
+/* Build the nanosvg implementation here, to build it only once and have other
+ * C files build fast during development. */
+#include <stdio.h>
+
+#define NANOSVG_IMPLEMENTATION
+#include "nanosvg.h"
+
+#define NANOSVGRAST_IMPLEMENTATION
+#include "nanosvgrast.h"

src/pbsplash.c

@@ -14,9 +14,7 @@
 #include <string.h>
 #include <math.h>
 #define NANOSVG_ALL_COLOR_KEYWORDS // Include full list of color keywords.
-#define NANOSVG_IMPLEMENTATION	   // Expands implementation
 #include "nanosvg.h"
-#define NANOSVGRAST_IMPLEMENTATION
 #include "nanosvgrast.h"
 
 #include "pbsplash.h"