[libc] Add malloc.h header defining mallopt (llvm#110908)

This patch adds the malloc.h header, declaring Scudo's mallopt
entrypoint when built LLVM_LIBC_INCLUDE_SCUDO, as well as two
constants that can be passed to it (M_PURGE and M_PURGE_ALL).

Due to limitations of the current build system, only the declaration
of mallopt is gated by LLVM_LIBC_INCLUDE_SCUDO, and the two new
constants are defined irrespectively of it. We may need to refine
this in the future.

Note that some allocators other than Scudo may offer a mallopt
implementation too (e.g. man 3 mallopt), albeit with different
supported input values. This patch only supports the specific case of
LLVM_LIBC_INCLUDE_SCUDO.

Author: fabio-d

libc/config/linux/aarch64/entrypoints.txt

@@ -347,6 +347,13 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wctob
 )
 
+if(LLVM_LIBC_INCLUDE_SCUDO)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # malloc.h external entrypoints
+    libc.src.stdlib.mallopt
+  )
+endif()
+
 set(TARGET_LIBM_ENTRYPOINTS
     # fenv.h entrypoints
     libc.src.fenv.feclearexcept

libc/config/linux/aarch64/headers.txt

@@ -11,6 +11,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.inttypes
     libc.include.limits
     libc.include.link
+    libc.include.malloc
     libc.include.math
     libc.include.pthread
     libc.include.signal

libc/config/linux/arm/entrypoints.txt

@@ -189,6 +189,13 @@ if(LLVM_LIBC_FULL_BUILD)
   )
 endif()
 
+if(LLVM_LIBC_INCLUDE_SCUDO)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # malloc.h external entrypoints
+    libc.src.stdlib.mallopt
+  )
+endif()
+
 set(TARGET_LIBM_ENTRYPOINTS
     # fenv.h entrypoints
     libc.src.fenv.feclearexcept

libc/config/linux/arm/headers.txt

@@ -4,6 +4,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.fenv
     libc.include.float
     libc.include.inttypes
+    libc.include.malloc
     libc.include.math
     libc.include.search
     libc.include.setjmp

libc/config/linux/riscv/entrypoints.txt

@@ -346,6 +346,13 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wctob
 )
 
+if(LLVM_LIBC_INCLUDE_SCUDO)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # malloc.h external entrypoints
+    libc.src.stdlib.mallopt
+  )
+endif()
+
 set(TARGET_LIBM_ENTRYPOINTS
     # fenv.h entrypoints
     libc.src.fenv.feclearexcept

libc/config/linux/riscv/headers.txt

@@ -11,6 +11,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.stdint
     libc.include.inttypes
     libc.include.limits
+    libc.include.malloc
     libc.include.math
     libc.include.pthread
     libc.include.sched

libc/config/linux/x86_64/entrypoints.txt

@@ -346,6 +346,13 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.wchar.wctob
 )
 
+if(LLVM_LIBC_INCLUDE_SCUDO)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # malloc.h external entrypoints
+    libc.src.stdlib.mallopt
+  )
+endif()
+
 set(TARGET_LIBM_ENTRYPOINTS
     # fenv.h entrypoints
     libc.src.fenv.feclearexcept

libc/config/linux/x86_64/headers.txt

@@ -13,6 +13,7 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.inttypes
     libc.include.limits
     libc.include.link
+    libc.include.malloc
     libc.include.math
     libc.include.pthread
     libc.include.sched

libc/include/CMakeLists.txt

@@ -146,6 +146,16 @@ add_header_macro(
     .llvm-libc-macros.limits_macros
 )
 
+add_header_macro(
+  malloc
+  ../libc/newhdrgen/yaml/malloc.yaml
+  malloc.h.def
+  malloc.h
+  DEPENDS
+    .llvm_libc_common_h
+    .llvm-libc-macros.malloc_macros
+)
+
 add_header_macro(
   math
   ../libc/newhdrgen/yaml/math.yaml

libc/include/llvm-libc-macros/CMakeLists.txt

@@ -109,6 +109,12 @@ add_macro_header(
     link-macros.h
 )
 
+add_macro_header(
+  malloc_macros
+  HDR
+    malloc-macros.h
+)
+
 add_macro_header(
   math_macros
   HDR