diff -ubBr --show-c-function /gnu/store/93z2pmmpla1n47q3xivqyic4mwvy0r5q-gcc-toolchain-8.4.0/include/c\+\+/x86_64-unknown-linux-gnu/bits/c\+\+config.h /gnu/store/xa45bzcbib4zqa7gk70nb35dzzwyr376-gcc-toolchain-7.5.0/include/c\+\+/x86_64-unknown-linux-gnu/bits/c\+\+config.h
--- /gnu/store/xa45bzcbib4zqa7gk70nb35dzzwyr376-gcc-toolchain-7.5.0/include/c++/x86_64-unknown-linux-gnu/bits/c++config.h	1970-01-01 01:00:01.000000000 +0100
+++ /gnu/store/93z2pmmpla1n47q3xivqyic4mwvy0r5q-gcc-toolchain-8.4.0/include/c++/x86_64-unknown-linux-gnu/bits/c++config.h	1970-01-01 01:00:01.000000000 +0100

[...]

@@ -644,61 +619,61 @@
 /* config.h.in.  Generated from configure.ac by autoheader.  */
 
 /* Define to 1 if you have the `acosf' function. */
-#define _GLIBCXX_HAVE_ACOSF 1
+/* #undef _GLIBCXX_HAVE_ACOSF */
 
 /* Define to 1 if you have the `acosl' function. */
-#define _GLIBCXX_HAVE_ACOSL 1
+/* #undef _GLIBCXX_HAVE_ACOSL */
 
 /* Define to 1 if you have the `aligned_alloc' function. */
 #define _GLIBCXX_HAVE_ALIGNED_ALLOC 1
 
 /* Define to 1 if you have the `asinf' function. */
-#define _GLIBCXX_HAVE_ASINF 1
+/* #undef _GLIBCXX_HAVE_ASINF */
 
 /* Define to 1 if you have the `asinl' function. */
-#define _GLIBCXX_HAVE_ASINL 1
+/* #undef _GLIBCXX_HAVE_ASINL */
 
 /* Define to 1 if the target assembler supports .symver directive. */
 #define _GLIBCXX_HAVE_AS_SYMVER_DIRECTIVE 1
 
 /* Define to 1 if you have the `atan2f' function. */
-#define _GLIBCXX_HAVE_ATAN2F 1
+/* #undef _GLIBCXX_HAVE_ATAN2F */
 
 /* Define to 1 if you have the `atan2l' function. */
-#define _GLIBCXX_HAVE_ATAN2L 1
+/* #undef _GLIBCXX_HAVE_ATAN2L */
 
 /* Define to 1 if you have the `atanf' function. */
-#define _GLIBCXX_HAVE_ATANF 1
+/* #undef _GLIBCXX_HAVE_ATANF */
 
 /* Define to 1 if you have the `atanl' function. */
-#define _GLIBCXX_HAVE_ATANL 1
+/* #undef _GLIBCXX_HAVE_ATANL */
 
 /* Define to 1 if you have the `at_quick_exit' function. */
-#define _GLIBCXX_HAVE_AT_QUICK_EXIT 1
+/* #undef _GLIBCXX_HAVE_AT_QUICK_EXIT */
 
 /* Define to 1 if the target assembler supports thread-local storage. */
 /* #undef _GLIBCXX_HAVE_CC_TLS */
 
 /* Define to 1 if you have the `ceilf' function. */
-#define _GLIBCXX_HAVE_CEILF 1
+/* #undef _GLIBCXX_HAVE_CEILF */
 
 /* Define to 1 if you have the `ceill' function. */
-#define _GLIBCXX_HAVE_CEILL 1
+/* #undef _GLIBCXX_HAVE_CEILL */
 
 /* Define to 1 if you have the <complex.h> header file. */
-#define _GLIBCXX_HAVE_COMPLEX_H 1
+/* #undef _GLIBCXX_HAVE_COMPLEX_H */
 
 /* Define to 1 if you have the `cosf' function. */
-#define _GLIBCXX_HAVE_COSF 1
+/* #undef _GLIBCXX_HAVE_COSF */
 
 /* Define to 1 if you have the `coshf' function. */
-#define _GLIBCXX_HAVE_COSHF 1
+/* #undef _GLIBCXX_HAVE_COSHF */
 
 /* Define to 1 if you have the `coshl' function. */
-#define _GLIBCXX_HAVE_COSHL 1
+/* #undef _GLIBCXX_HAVE_COSHL */
 
 /* Define to 1 if you have the `cosl' function. */
-#define _GLIBCXX_HAVE_COSL 1
+/* #undef _GLIBCXX_HAVE_COSL */
 
 /* Define to 1 if you have the <dirent.h> header file. */
 #define _GLIBCXX_HAVE_DIRENT_H 1