[gn build] Make HAVE_MALLINFO2 a gn arg, default to false

[aeubanks]

Summary

D117916 broke some people because some distros are still using a glibc
older than 2.33. Add gn arg llvm_have_mallinfo2 and default to false for
now.

[peterwaller-arm]

👍 thanks.

Looks like the build is broken due to PPC_LINUX_DEFAULT_IEEELONGDOUBLE, but reverting 08e535a50797, this differential fixes it.

[pcc]

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

52

Shouldn't the default be true? If the default assumption that we make in the gn build is that glibc is up to date, users of older glibc should be the ones who need to request the non-default behavior.

[aeubanks]

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

52

The question is which default inconveniences the fewest people. It probably makes sense to set this to true by default now: https://reviews.llvm.org/D126415

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

 # become declare_args if anyone wants to set them.
 
 declare_args() {
   # Enable additional checks that alter the LLVM C++ ABI.
   llvm_enable_abi_breaking_checks = llvm_enable_assertions
 
   # Iterate unordered llvm containers in reverse.
   llvm_enable_reverse_iteration = false
+
+  # glibc is at least 2.33 which has mallinfo2.
+  # TODO: remove this once nobody using the gn build is building against an old glibc.
+  llvm_have_mallinfo2 = false
 }
 
 write_cmake_config("abi-breaking") {
   input = "abi-breaking.h.cmake"
   output = "$target_gen_dir/abi-breaking.h"
   values = []
 
   if (llvm_enable_abi_breaking_checks) {
write_cmake_config("config") {
   ]
 
   if (current_os == "linux" || current_os == "android") {
     values += [
       "HAVE_FUTIMENS=1",
       "HAVE_LINK_H=1",
       "HAVE_LSEEK64=1",
       "HAVE_MALLINFO=1",
-      "HAVE_MALLINFO2=1",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=1",
     ]
   } else {
     values += [
       "HAVE_FUTIMENS=",
       "HAVE_LINK_H=",
       "HAVE_LSEEK64=",
       "HAVE_MALLINFO=",
-      "HAVE_MALLINFO2=",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=",
     ]
   }
 
   if (current_os == "mac") {
     values += [
       "HAVE_CRASHREPORTER_INFO=1",
       "HAVE_DECL_ARC4RANDOM=1",
if (llvm_enable_zlib) {
     values += [ "LLVM_ENABLE_ZLIB=" ]
   }
 
   if (llvm_enable_libxml2) {
     values += [ "LLVM_ENABLE_LIBXML2=1" ]
   } else {
     values += [ "LLVM_ENABLE_LIBXML2=" ]
   }
+
+  if (llvm_have_mallinfo2) {
+    values += [ "HAVE_MALLINFO2=1" ]
+  } else {
+    values += [ "HAVE_MALLINFO2=" ]
+  }
 }
 
 write_cmake_config("llvm-config") {
   input = "llvm-config.h.cmake"
   output = "$target_gen_dir/llvm-config.h"
   values = [
     "LLVM_BUILD_LLVM_DYLIB=",
     "LLVM_BUILD_SHARED_LIBS=",