bootstrapping: drop grep/gawk build-requirement

Per pull-request #2 discussion.

gawk.spec

@@ -45,16 +45,14 @@ Source0:          https://ftp.gnu.org/gnu/gawk/gawk-%{version}.tar.xz
 Source1:          LICENSE.GPLv2
 Source2:          LICENSE.LGPLv2
 Source3:          LICENSE.BSD
+Source4:          get_api_version.sh
 
 Provides:         /bin/awk
 Provides:         /bin/gawk
 
 # Extraction of API major & minor versions, so we can export them below.  Put
 # this below Source0 definition to have %%SOURCE0 defined.
-%{expand:%(
-    tar xf %{SOURCE0} '*/gawkapi.h' --to-stdout 2>/dev/null | \
-    awk '/define\ gawk_api_/ {print "%%global " $2 " " $3 }'
-)}
+%{expand:%(%{SOURCE4} %{SOURCE0})}
 
 Provides:         gawk(abi) = %{gawk_api_major_version}.%{gawk_api_minor_version}
 
@@ -66,7 +64,6 @@ Requires(preun):  info
 
 BuildRequires:    ghostscript-core
 BuildRequires:    git
-BuildRequires:    grep
 
 # Extending GAWK possibilities:
 BuildRequires:    libsigsegv-devel

get_api_version.sh

@@ -0,0 +1,11 @@
+#! /bin/sh
+
+tar xf "$1" '*/gawkapi.h' --to-stdout | \
+while read line; do
+    set -- $line
+    case $2 in
+    gawk_api_*_version)
+        echo "%global $2 $3"
+        ;;
+    esac
+done