doc: Fix some broken links

docs/markdown/Compiler-properties.md

@@ -3,7 +3,7 @@
 Not all compilers and platforms are alike. Therefore Meson provides
 the tools to detect properties of the system during configure time. To
 get most of this information, you first need to extract the *[compiler
-object](Reference-manual_returned_compiler.html)* from the main
+object](Reference-manual_returned_compiler.md)* from the main
 *meson* variable.
 
 ```meson

docs/yaml/objects/external_program.yaml

@@ -18,7 +18,7 @@ methods:
     **NOTE:** You should not usually need to use this method. Passing the
     object itself should work in most contexts where a program can appear,
     and allows Meson to setup inter-target dependencies correctly (for
-    example in cases where a program might be overridden by a [[build_tgt]]).
+    example in cases where a program might be overridden by a [[@build_tgt]]).
     Only use this if you specifically need a string, such as when embedding
     a program path into a header file.
 
@@ -45,7 +45,7 @@ methods:
     **NOTE:** You should not usually need to use this method. Passing the
     object itself should work in most contexts where a program can appear,
     and allows Meson to setup inter-target dependencies correctly (for
-    example in cases where a program might be overridden by a [[build_tgt]]).
+    example in cases where a program might be overridden by a [[@build_tgt]]).
     Only use this if you specifically need a string, such as when embedding
     a program path into a header file.