Fixed glibc compatibility by hardcoding lower version for log2

fixes #1690

- the minimum glibc version was inadvertently bumped in the latest
  release because `log2` was linked to a higher version
- this adds the downgrade to the gcc preinclude file to resolve this
- in an upcoming commit, we will add a test to prevent these issues from
  occurring again

src/gcc-preinclude.h

@@ -12,6 +12,7 @@
 __asm__(".symver memcpy,memcpy@GLIBC_2.2.5");
 __asm__(".symver exp,exp@GLIBC_2.2.5");
 __asm__(".symver log,log@GLIBC_2.2.5");
+__asm__(".symver log2,log2@GLIBC_2.2.5");
 __asm__(".symver pow,pow@GLIBC_2.2.5");
 __asm__(".symver fcntl64,fcntl@GLIBC_2.2.5");
 #endif
@@ -20,6 +21,7 @@ __asm__(".symver fcntl64,fcntl@GLIBC_2.2.5");
 __asm__(".symver memcpy,memcpy@GLIBC_2.17");
 __asm__(".symver exp,exp@GLIBC_2.17");
 __asm__(".symver log,log@GLIBC_2.17");
+__asm__(".symver log2,log2@GLIBC_2.17");
 __asm__(".symver pow,pow@GLIBC_2.17");
 __asm__(".symver fcntl64,fcntl@GLIBC_2.17");
 #endif