meson: Use configuration_data() instead of piping variables through echo

Having a template file with replacement macros is a bit cleaner than
encoding the setup of the file in `meson.build` and piping that through
`echo` with caputred variables.

Unfortunately there appears to be no support for repetition, to e.g.
expand a list of platform names into the various uses (array with comma-
separation, or individual `extern struct` declarations, forcing us to
have some form of string expansion within `meson.build`).

meson.build

@@ -33,7 +33,7 @@ debugcc_srcs = [
   ]
 
 platform_defs = []
-platform_array = ['const struct debugcc_platform *platforms[] = {']
+platform_array = []
 
 foreach p: platforms
   debugcc_srcs += p + '.c'
@@ -45,19 +45,14 @@ foreach p: platforms
     pointing_to: 'debugcc')
 endforeach
 
-platform_array += '\tNULL,'
-platform_array += '};'
+platforms = configuration_data()
+platforms.set('PLATFORM_DEFS', '\n'.join(platform_defs))
+platforms.set('PLATFORM_ARRAY', '\n'.join(platform_array))
 
 debugcc_srcs += configure_file(
+  input: 'platforms.c.in',
   output: 'platforms.c',
-  capture: true,
-  command: ['echo',
-    '/* Autogenerated file, do not edit */\n\n' +
-    '#include <stdlib.h>\n\n' +
-    '\n'.join(platform_defs) +
-    '\n\n' +
-    '\n'.join(platform_array)
-    ])
+  configuration: platforms)
 
 executable('debugcc',
   debugcc_srcs,

platforms.c.in

@@ -0,0 +1,9 @@
+/* Autogenerated file, do not edit */
+#include <stdlib.h>
+
+@PLATFORM_DEFS@
+
+const struct debugcc_platform *platforms[] = {
+@PLATFORM_ARRAY@
+	NULL,
+};