Don't make up names with double underscores

They're reserved for use by the compiler, standard library, etc.

Bug: None
Change-Id: I3b5106473b52847b9de406aaab307909b5378dba
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183440
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32038}

system_wrappers/source/cpu_features_linux.c

diff --git a/system_wrappers/source/cpu_features_linux.c b/system_wrappers/source/cpu_features_linux.c
index 004de5a..37739c1 100644
--- a/system_wrappers/source/cpu_features_linux.c
+++ b/system_wrappers/source/cpu_features_linux.c
@@ -11,10 +11,14 @@
 #include <stdlib.h>
 #include <string.h>
 #include <features.h>
-#ifndef __GLIBC_PREREQ
-#define __GLIBC_PREREQ(a, b) 0
+
+#ifdef __GLIBC_PREREQ
+#define WEBRTC_GLIBC_PREREQ(a, b) __GLIBC_PREREQ(a, b)
+#else
+#define WEBRTC_GLIBC_PREREQ(a, b) 0
 #endif
-#if __GLIBC_PREREQ(2, 16)
+
+#if WEBRTC_GLIBC_PREREQ(2, 16)
 #include <sys/auxv.h>
 #else
 #include <fcntl.h>
@@ -22,6 +26,7 @@
 #include <errno.h>
 #include <link.h>
 #endif
+
 #include "rtc_base/system/arch.h"
 #include "system_wrappers/include/cpu_features_wrapper.h"
 
@@ -33,7 +38,7 @@
   int architecture = 0;
   unsigned long hwcap = 0;
   const char* platform = NULL;
-#if __GLIBC_PREREQ(2, 16)
+#if WEBRTC_GLIBC_PREREQ(2, 16)
   hwcap = getauxval(AT_HWCAP);
   platform = (const char*)getauxval(AT_PLATFORM);
 #else
@@ -57,7 +62,7 @@
     }
     close(fd);
   }
-#endif  // __GLIBC_PREREQ(2,16)
+#endif  // WEBRTC_GLIBC_PREREQ(2, 16)
 #if defined(__aarch64__)
   architecture = 8;
   if ((hwcap & HWCAP_FP) != 0)