build: allow any GCC version

The existing test didn't work on modern GCC; a clean fix didn't work
on modern macOS due to its aliasing gcc to clang; and the test being
done is for a version of GCC from 2013 that doesn't ship on any modern
Linux system. (RHEL7 is on GCC 4, but hasn't shipped the buggy version
either ever or since 2015, depending on which source material I look
at.)

Closes #2023

build.sh

@@ -132,23 +132,6 @@ semver_into() {
     fi
 }
 
-# issue 1440
-gcc_version_ok() {
-    GCC_VERSION=`gcc -dumpversion`
-    local GCC_MAJOR local GCC_MINOR local GCC_PATCH local GCC_SPECIAL
-    semver_into $GCC_VERSION GCC_MAJOR GCC_MINOR GCC_PATCH GCC_SPECIAL
-
-    if [[ $GCC_MAJOR -lt 4
-        || ( $GCC_MAJOR -eq 4 && $GCC_MINOR -lt 7 )
-        || ( $GCC_MAJOR -eq 4 && $GCC_MINOR -eq 7 && $GCC_PATCH -lt 3 )
-        || ( $GCC_MAJOR -eq 4 && $GCC_MINOR -eq 8 && $GCC_PATCH -eq 0 )
-        ]] ; then
-        echo "gcc version required >= 4.7.3, != 4.8.0, >= 4.8.1, got $GCC_VERSION"
-        return 1
-    fi
-    return 0
-}
-
 clang_version_ok() {
     CLANG_VERSION=`clang --version | head -n1`
     CLANG_VERSION_RE='^[a-zA-Z0-9 ]* version (.*)$' # 3.3-5
@@ -177,7 +160,7 @@ set_cc() {
     fi
 
     test_programs_installed gcc g++
-    if [[ $? -ne 0 ]] && gcc_version_ok ; then
+    if [[ $? -ne 0 ]] ; then
         [ -z "$CC" ] && CC=gcc
         [ -z "$CXX" ] && CXX=g++
         return