Revert "Merge commit '8e97a8c6'"

This reverts commit 1a4315f2, reversing
changes made to 869401ce.

At least one distro (Arch) ships gsm.h inside the gsm/ folder

configure

@@ -1922,6 +1922,7 @@ HEADERS_LIST="
     dxgidebug_h
     dxva_h
     ES2_gl_h
+    gsm_h
     io_h
     machine_ioctl_bt848_h
     machine_ioctl_meteor_h
@@ -5921,7 +5922,9 @@ enabled libfreetype       && require_pkg_config libfreetype freetype2 "ft2build.
 enabled libfribidi        && require_pkg_config libfribidi fribidi fribidi.h fribidi_version_info
 enabled libgme            && { check_pkg_config libgme libgme gme/gme.h gme_new_emu ||
                                require libgme gme/gme.h gme_new_emu -lgme -lstdc++; }
-enabled libgsm            && require libgsm gsm.h gsm_create -lgsm
+enabled libgsm            && { for gsm_hdr in "gsm.h" "gsm/gsm.h"; do
+                                   check_lib libgsm "${gsm_hdr}" gsm_create -lgsm && break;
+                               done || die "ERROR: libgsm not found"; }
 enabled libilbc           && require libilbc ilbc.h WebRtcIlbcfix_InitDecode -lilbc $pthreads_extralibs
 enabled libkvazaar        && require_pkg_config libkvazaar "kvazaar >= 0.8.1" kvazaar.h kvz_api_get
 # While it may appear that require is being used as a pkg-config

libavcodec/libgsmdec.c

@@ -27,7 +27,12 @@
 
 // The idiosyncrasies of GSM-in-WAV are explained at http://kbs.cs.tu-berlin.de/~jutta/toast.html
 
+#include "config.h"
+#if HAVE_GSM_H
 #include <gsm.h>
+#else
+#include <gsm/gsm.h>
+#endif
 
 #include "libavutil/channel_layout.h"
 #include "libavutil/common.h"

libavcodec/libgsmenc.c

@@ -27,7 +27,12 @@
 
 // The idiosyncrasies of GSM-in-WAV are explained at http://kbs.cs.tu-berlin.de/~jutta/toast.html
 
+#include "config.h"
+#if HAVE_GSM_H
 #include <gsm.h>
+#else
+#include <gsm/gsm.h>
+#endif
 
 #include "libavutil/common.h"