[libc] Fill out generated malloc.h and related stdlib.h extensions

libc/include/malloc.yaml

@@ -9,10 +9,23 @@ macros:
   - macro_name: M_PURGE_ALL
     macro_header: malloc-macros.h
 functions:
+  - name: malloc_usable_size
+    standards:
+      - gnu
+    return_type: size_t
+    arguments:
+      - type: void *
   - name: mallopt
     standards:
       - gnu
     return_type: int
     arguments:
       - type: int
       - type: int
+  - name: pvalloc
+    standards:
+      - bsd
+      - gnu
+    return_type: void *
+    arguments:
+      - type: size_t

libc/include/stdlib-malloc.yaml

@@ -1,4 +1,10 @@
 # This file has declarations that appear both in <stdlib.h> and in <malloc.h>.
+# These include the subset of GNU extensions that Scudo supports.
+#
+# Note: glibc's <stdlib.h> and <malloc.h> both also have `reallocarray`,
+# which Scudo does not support and is omitted here.  (Each of those glibc
+# headers also has related functions the other lacks, but those should be
+# covered separately in stdlib.yaml and malloc.yaml instead.)
 
 functions:
   - name: aligned_alloc
@@ -27,18 +33,24 @@ functions:
     return_type: void *
     arguments:
       - type: size_t
+  - name: memalign
+    standards:
+      - gnu
+    return_type: void *
+    arguments:
+      - type: size_t
+      - type: size_t
   - name: realloc
     standards:
       - stdc
     return_type: void *
     arguments:
       - type: void *
       - type: size_t
-
-# Note: glibc's <stdlib.h> and <malloc.h> both have these, which are
-# currently missing here:
-#  - name: reallocarray
-#  - name: memalign
-#  - name: valloc
-# Each of those glibc headers also has related functions the other lacks.
-# Only the common subset is mentioned here for future consideration.
+  - name: valloc
+    standards:
+      - bsd
+      - gnu
+    return_type: void *
+    arguments:
+      - type: size_t

libc/include/stdlib.yaml

@@ -127,6 +127,14 @@ functions:
     arguments:
       - type: long long
       - type: long long
+  - name: posix_memalign
+    standards:
+      - posix
+    return_type: int
+    arguments:
+      - type: void **
+      - type: size_t
+      - type: size_t
   - name: qsort
     standards:
       - stdc